The stuff is definitely super hardy! I have it everywhere in my tank. After scraping it off it seems to come back. Seems like if you don't get every tiny speck off it comes back! So aggravating.
I'm trying to get mine to grow up the back wall as well. I've peeled it off of smooth surfaced rocks before very easily with my fingernails. I'm thinking it would be much easier to contain being on the glass. I had to isolate mine to one rock and I set it on the sand by the back glass and side wall. I think it would be cool to see it grow on the side glass as well! You could outline it with a marker and watch it grow outside the lines. Lol.
With it being on the back glass you could shape it however you want so it doesn't look like just a big blotch of green. Make it grow in lines, or shape it into a cool design... That's what I want to do with it anyway.