pulley

What should I do? I have my chain tensioner centered almost perfectly so that the chain isn't on one side more than the other and come off part of the rear sprocket, and also, I have the tensioner wheel set a little above so that the wheel spins, but since I don't think my rear sprocket is...

So I'm installing a motor on my bike this weekend, and I've been reading up on all the problems I might run into. I noticed that the chain tensioner seems to be almost universally hated because it comes loose and falls into the spokes and makes you crash. So I've been trying to think of ways to...