Question on water heater for turtle?

We had a friend giving away his turtle, he lost interest and didn't want to care for it anymore. We went out and bought all the supplies needed (I think) We have a 25 gallon tank, filter, heater, turtle dock, UV light, and heat lamp. I've also bought a water heater but I have a question about it, I bought a 25 gallon heater, but its very tall. The top can't be submerged but when the water is at the minimum height, it makes the turtle dock too high and close to the heat lamp. Do they make heaters out there that can lay down and is completely submersible?