This idea came from "Laidback" on Icefrogs blog. However, I don't know if you can actually do it without giving control of the sentinel to the players.
And I also got an idea for DotA. I think it would be helpful if you could put Glyph of Fortification icon on every tower. So you don't need to click on your Circle of Power everytime to use GOF, just click on the tower that is attacked/occupied..
Thoughts? I just think it would be much easier to use that way.