The reason the tensioner pulls toward the inside is that the chain is misaligned. If the front and rear sprockets are lined up correctly, and the tensioner pulley is straight, you'll never have a problem if the bracket is tight. Get some good quality bolts and locknuts. Sometimes, the bracket needs to be bent a little due to the angle of the chainstay. You want the pulley inline with the chain itself, not the chainstay. There is always the old trick of staking the bracket, which involves drilling a small (the smaller the better) hole and installing a drift pin, which will stop any movement of the bracket, but could weaken the chainstay. The best solution is to make or purchase a spring-loaded tensioner, which has enough movement built in to correct any minor misalignment in the chain or rear sprocket. The rear sprocket is a common problem area, as it is near impossible to get it perfectly centered.