Welcome to the Forum!
I like the foam idea so much but I haven't done it yet myself. I like the idea of being able to make tunnels and stuff. It does seem like a really hard material to work with though. Like it looks like it would get everywhere
What size enclosure is he in? How's his poops? Any other abnormalities or symptoms? He looks healthy. While the surfing is stressful for you and maybe a little for him it is a good sign of physical activity. That means he's healthy.
You could put a waterfall in as long as caleb is protected from drowning. Make sure she can easily escape the water. With that being said this isn't something I'd generally recommend for a beginner gecko keeper. it's hard to clean. Difficult to maintain and an additional risk for your gecko