A few other random ideas...
Mana Short, when cast upon, the resistee(target) rolls his magic defense score and adds that to the caster's casting target, potentially causing failures or inflicting fatigue. This is similar, but different from regular Magic Resistance. Might also require the "raising" of some sort of magical ward with a duration of Diameter or some associated cost depending on the tradition. Additional variants might not prevent the spell from being successfully cast, but inflict additional levels of fatigue, roughly 1 per extra 10 by which it failed. There are some existant spell types with similar charts (tablets?) I forget which now, though.
A different form of Magic Resistance which would need a disambiguating name that would reduce the effect of spells cast at the resistee based on a skill (as appropriate to the spell/effect in question). If implemented as an ability some simple rules guidelines would be to have the effects of the spell reduced by the ability score. For straight damage spells this is simply a form of soak. For other spells the levels would reduce, first, the target if the target was larger then individual (so the spell would effect everyone but the target), next priority would be to reduce the duration by one magnitude per 5 ranks in the ability or fraction thereof (unless the effect was momentary). If neither of these traits can be overridden then the spell's base effect is reduced by SG interpretation, with the guideline that if the spell's base level can be matched by the resistance ability, the spell simply fails, otherwise you get reduced effect. So, for instance, "Loss of but a Moment's Memory" resisted by a rank 5 of this sort of resistance might only erase the last 2m of memory, or cause memories to be erased but slowly re-emerge as if the target were waking abruptly from a dream and having to piece together where they were and what was happening, or the inverse where the memories of the past five minutes fade like a dream where the target had only a round in which to pick one or two important thoughts to hold onto before they all faded.
Another type which I'm using in my current saga is the juju doll. That's not what I call it, but it's a secret in my game and the actual name would tell my players too much . But the idea is that the caster creates a symbolic and arcane connection to himself in the form of an idol which then acts as the first recipient of spells targeted at him (but not area effect targets). The doll takes vis and a season to construct, and by skill/lore it can only block certain forms (elemental, herbem, animal, corpus and mentem in order of difficulty, roughly). In my saga the doll can soak so much damage (again based on skill/vis expended in creation) and an otherwise unlimited number of levels of non-damage spells, although you could obviously introduce an overall spell level limit on absorption. The flaws for this resistance include its inability to protect against indirect, ae spells, including group target spells (unless the group is at its limit, then the target might get lucky), the idea being that the beneficiary of the doll is in a group with the doll, so an individual spell will hit the doll (that's its point), but a group spell will hit them both. Other flaws are, obviously, that the doll is a physical object and a profound arcane connection to the beneficiary (in the same manner as runes of a Viktir), so the doll must be carefully hidden. Carrying the doll is suboptimal as many spells (e.g. Pilum of Fire) would effectively hit the caster even redirected at the doll.
Grounding. Allow an interrupt style "magical dodge", where the defender forgoes casting in a round and instead makes a magical defense roll to redirect or shut down the spell. You could have two different version, one of which, similar to hermetic fast cast counter magics, tries to directly assault and shut down the spell (or ground it). A second more "watery" style would be to have the defender actually redirect the spell with a degree of control based on how well he beat the caster's finesse total (fun for those finesse-less pilum users), allowing him to subvert the target of the spell by magnitude of success to a nearby friendly (ah the moral dilemma's), an innocuous target, a strategic target/bystander, a strategic bystander, an enemy, the caster. (That's five magnitudes range total-0 Friendly, 1 Innocuous, etc.). The definitions of what is innocuous, what is strategic, etc. are based on the perceptions of the caster (since that's who's targeting is being subverted). So a barrel filled with greek fire might seem an innocuous target to the caster if he didn't know what was in it.
Then there are all sorts of colorful defenses you could envision that may or may not fit your themes. Spirit dopplegangers, where the target's actual "self"/spirit is displaced from their body, making magics run awry (similar to the meta-magic equivalent of Wizard's Sidestep), causing the first spell cast by an unsuspecting caster to fail outright and subsequent spells to take finesse or casting total penalties. You could have some fun with this, with meta spells building upon this idea both offensively and defensively, trying to spot waldo as it were, who might be displaced, masked as the spirit of something else with false additional spirit signatures implanted in the scene to throw off would be circumventionist detection spells.
You could also have the miasma resistance cloud. This would increase the fatigue cost of all spells cast on the target based on the puissance of the cloud. Masters of this defense might increase the cost to cast on them to five or more fatigue levels. Again, you could get detailed with the cat and mouse of it, allowing spells which directly attack and disperse the cloud (1 fatigue cost level at a time). You could also have the cloud naturally weaken by 1 level for each spell cast through it (potentially in either "direction"). The cloud's maximum level might be determined by an ability and require a day per level to restore or build up. Obvious defects could include an inability to affect item effects. It could also be two way, so that the creator of the cloud could not cast "out" without also paying the additional fatigue cost.
And on and on.... Really I'd say you want to list out all the traditions/people you want to create some form of magic resistance for and try to make something that stylistically matches their theme.