I've seen a number of posts from those with issues related to chain tensioners not gripping the frame well. The best solution that I've come up with is some rubberized/fiber reinforced gasket material from my local auto parts store. it's only a few bucks for a pretty good sized sheet and simply cutting a couple of pieces to line the inside of the bracket where it comes in contact with the frame seems to provide a really good grip.
I've also used this to line the motor mounts and clamps which provides the added benefit of reducing vibration considerably as well.
Happy riding to all!!