Circular Wards and movable rings

I am playing a mage who has taken a minor magical focus in circular wards. I would like to use these skills to their optimum level. My GM had advised me that I might be interested in creating a talisman in the form of a shield, and that I even might be able to use the circular shape of the shield to cast my circle target spells. (i.e. placing the shield on the ground, inscribing it and then using muto to increase its size.

Even though this conversation might be moot since the GM has final say in whether or not it's possible to move a circular ward without breaking the enchantment, but I wanted to get a sense of how this might have effected or been used in other sagas. I'm specifically asking about inscribing on items that are circular, i.e. Shields, hoops, enchanted rope, rings, etc. and moving them. Not pulling any weird Rego Vim, move the locus of the spell or something.

Heh...I guess we were writing at the same time.