I dont put enough glue on, use too big of a patch, the ends arent securely fastened, and dont hold it 5 minutes and I never have problems. I do sand it pretty well, though. I would look above and make sure you are getting over the hole well.
Also, when your patches 'fail', do you pull it out and look? is it a new hole, does the patch come off? I mean, what do you consider a 'failure'?