BTR, a ring is "drawn", not fabricated. One could draw a ring on anything, including an iron hoop, or a chunk of solid bedrock.
But "breaking" something that is drawn such as a circle or pentagram could be as simple as laying a stick across it- such has been traditional canon for various fantasy literature, tho' I'm less certain about actual historical arcane beliefs (and it's been a while since I read The Golden Bough.)
I recall reading somewhere that Ring Duration and Circle Target were tied to the earth.
For example, if I'm on a ship and use a Ring/Circle spell, as soon as the ship moves, the effect is broken. In fact, that was the example used.
Am I making this up or was it just an argument I agreed with on some board/list and thought I read it in a book?
The Ring can be pre-existing (thus the practice of insetting rings into laboratories) but the whole ring must be traced and concentration rolls done on specific intervals.
Further, it's only everything inside the ring. You'd get the foundation to rip out of the ground inside the ring (and pray that the tremors don't warp your substance too much out of shape) and move up into the sky, but if you try to move it to the side...out of the effect...
Considering that the wards state that they show as domes, it could be safe to say that they have limits in the vertical too...
But I think the ruling about not being able to move a ring sounds good - for game balance if notthing else.