30 years, no problems. Installed a new liner 2.5 years ago and now it has a 1" sagging wrinkle on bottom of the shallow end, right before deep end. You can see it stretching/slipping from the bottom corners...upon installation they put foam on bottom to "try" to smooth it out, but the texture looks terrible! Had plumber out today to unplug a clogged drain, which is what the pool guy suspected...water undernieth, but we wonder if it's really an issue of poor installation, or because it's sliding on the foam on the bottom... please HELP!!!