Hey guys,
An update here. I bought replacement suction cups and they lasted very little time before they, too, failed.
I also read more about wedging cork bark into the tank as a basking platform, but a few people said they ended up expanding and, over time, cracking their aquariums and causing them to leak (this in a 90-gallon tank = no good!). :-/ I'm on a budget, so replacing the cork every three months isn't an attractive option, either.
So I contacted K&J Magnetics. They sell the big neodymium magnets, coated with plastic for aquarium use. They even have a page devoted to aquarium magnets: (
http://www.kjmagnetics.com/blog.asp?p=aquarium) and the problem of leverage: (
http://www.kjmagnetics.com/blog.asp?p=leverage).
The problem (other than that the super-strong magnets I'd need probably at least four of would be $25 EACH!) is that the basking platform's ramp is so long, making it much easier for leverage to pry the magnets off the wall.
The engineers at K&J said if I could rest the bottom of the platform on something, I might still be able to use the magnets. I bought the large 90-gallon tank so the turtles could have plenty of room to swim, and the water level is too high to rest it on the bottom of the tank. (Can't make the water level much lower or the filter output will be exposed, splashing water everywhere.)
**SO THE QUESTION IS**:Any suggestions for something I could put in the tank to rest the bottom of the platform on? I guess I need something about 12 - 16" tall. Not sure how to find a tall narrow sturdy rock with a flat top, which would be ideal!

Maybe just look around the park for a couple of huge flat-topped rocks? OR--is there some man-made object that wouldn't harm the turtles?