Your going to have to get a different basking area. This seems like a pretty popular subject on this forums. Theres been a couple of members here that have had the same issue. I'd recommend this ramp
http://www.petmountain.com/show_product/11442-503833 They have it in small, med, and large sizes. It's what I have for my RES, I have the large one and it's still holding her without issue, she's 5-6 inches. It also has a ramp that extends into the water, where she likes to sleep at night.