Well you won't want to hear it, but if you can't get to the pipes from behind the wall, you'll have to do it the hard way. First though, check the valve stems to make sure they're not causing the leaking and the watter is running back into the wall from them. If you have a single handle faucet, you should be able to see into the wall by removing the round cover. If all else fails, you'll likely have to pull the shower wall (or stall if it's one piece). Since I have no way of knowing what kind of shower stall you have, you'll just have to study it closely to determine the least destructive method. I don't think you'll want to cut a hole through the shower wall - sealing it back up could be hard or impossible. Hopefully, with a little patience and care you'll be able to remove and reuse the old shower stall. NOTE: Before pulling out the old stall, make sure all the plumping handles and shower head pipe are removed. Good Luck!