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I bought one of those floating basking docks that attach to the side of the tank with suction cups. I used it for a couple of days, when I noticed the small RES were getting caught in the bars that hold the dock to the sides. Do you think they would get traped? Or is it just me? I really would like to use the dock. The RES are about 3to4 inches.

Welcome!
Yes, they can get stuck.
To prevent this, there are two things you can do:
Turn the bars upside-down, so the horizontal bar is at the top instead of under water.
Take the bottom suction cups off. The suction cups at the top should be enough to hold the dock in place.

Yes, little ones tend to squeeze their shells into dangerous predicaments. What I would suggest is to either remove the bottom suction cups to afford the plastic bars more flexion so your RES can escape by pushing against the glass. You can also stick suction cups to block the space between the bars and glass, but this will eventually obstruct the dock's capacity to lower with the water line. Also make sure the horizontal bar is above the water. If it's not, reverse it so it is.

Filbert used to try to get behind the bars of his dock when I first got it. Luckily, he was able to get himself out of it. He did stop trying to get back there... eventually.

My turtles used to use it to scratch their backs.....They never got stuck

I have a client who's turtle got stuck and nearly drown. She had to do cpr to revive him. Luckly she found him quick enough. So she cut the bar off

Thank you all very much, I will difinitley redo the bars on the dock as you suggest. I bought them at a pet shop, they were in 1 inch of water. I filled the tank almost full when I got them and installed the dock after all thier struggling I decided they couldn't swim. It has taken a while for them to learn to swim and have the stength to get around for very long without coming up for air. I was afraid they would drown if they got caught in the bars. But I guess the real problem is I have it put together wrong. I have gradually been raising the water level, it is about 6 inches deep now, but I have a lot of rocks and plants in the tank they can get a hold of and come up for air. How long do you think it will take them to become strong swimmers? I have had them about 3 weeks. I would like to get rid of a lot of the rocks and give them more room to swim and put the dock back in so that I can get them closer to the lights.

I'd say put the dock back get rid of most of the rocks and get floating plants. At that size they should be fine.

I would fill the tank up, place the dock in with the frame upside down like Bulldog suggested, then put some fake plants in the tank. This will provide resting spots for them and they wont be able to get caught into anything. You can also put in some floating plants like lily pads. If your turts are 3-4 inches long, they'll be able to figure out swimming rather quickly.