+1!
(and only because "+1" is all I can reasonable add!)
Most everything that can be said has been posted above, or in one of these:
o Here's a recent thread on the same topic - On Wards - #3 by Cuchulainshound
o Here's one on "Are wards mobile", but the many of the points raised are directly relevant to your question - Circular Wards: Mobile? - #4 by SpoonR
o Yet another: https://forum.atlas-games.com/t/the-break-room/102/1
o Here's an old one w/ some other Q's tossed in - Rings and Circles - #8 by Furion_Transsanus
But 3 important points -
A (Hermetic) mage cannot (with rare exceptions) use Creo to create things with any Target other than Individual or Group - don't let your Players confuse Duration:Ring and Target:Circle on this point. (I want to say that there is a canon example (somewhere) that goes directly contrary to the above - forget where. Ignore it at your discretion, but with many blessings.)
Also, "Wards" may use Circle/Ring, but that doesn't mean they have to work the same as any "normal" spell w/ Ring Duration - that's up to you/the Troupe. Wards have their own little subsection of the rules (p 114), and so a different call can be made on those without worrying too much about it. (Some of the threads I linked above talk about Wards specifically, but the questions/considerations are parallel.)
Lastly, whatever you decide, take it to a logical extreme before finalizing it. Consider "permanent" rings (magically inlaid metal, massive stone constructions, etc etc), rings inscribed on wagons or sailing ships, on tattoos, on cloaks, on rings, on walls, ceilings, carpets, sails - huge, tiny, mobile, flexible, on skin, on a Familiar's hide - the works - because once you rule on it, the Players will start thinking about how to use it. Make sure you, as SG, will be both comfortable and consistent in whatever may come down the pipe later from your ruling. 