Aquatic Pond Turtle: She is too heavy for the tank docks and you give me...?

links to tank supplies for the turtle docks they have in the tanks at the fish or reptile stores? I need something sturdy. My pond turtle is in a tank and she can't get out of the water to bask because she falls off the dock. I have bought the largest dock in the store along with a a hollow log that floats and its pretty big..and she just can't do it. I need a solid rock that will stay in position and she can just climb up onto but nothing that floats. Those don't agree with her. Thanks!