Looking for filter suggestions

I need suggestions for filtering large turtle tanks.
As you know, turtles are very messy; bits of skin, solid poop, and so forth will clog many filter designs, and cause them to stop working. I have found, however, that sponge filters with power heads do not clog, and are an ideal submersible filter. Unfortunately, my snapping turtles like to eat sponge filters.
Does anybody have any suggestions for an economical filter that does not clog, and that snapping turtles do not eat? I need something submersible that will work in poly stock tanks.

How many gallons?

They are in poly tanks. Water volume is generally between 20-75 gallons.

I read that, wasn't sure how high you were going to fill it. I'd say two Aqueon QuietFlow internal power filter (AT40) less than $30 ea..or a Laguna® pond filter if you want something more powerful and are willing to pay a lil' more. Me personally, I'd go with a pond filter for a poly tank. Those Aqueon filters are ok, but you'll probably have to de-clog every few days.

Hello, I use a Hydor 600 professional canister filter on my 90 gallon tank filled with about 60 gallons of water and have had good success. They come in a variety of sizes. The 600 cost about $159.00. Hope this helps.

You can always build on out of a five gallon buck filled with scrubbies. Use a nice tetra pond pump (the best I've ever used) and pump the water through the top, down to the bottom using some PVC, then let the water come back up to the top and out the side back into their poly tank. Have a mechanical filter somewhere in between those 2, maybe as a prefilter or some sort since there's probably not enough room for a small skimmer.
If those don't work, then a fluval Fx series filter would be the absolute best, although they are like $300.

In use a Fluval FX5 in my 120 gallon tank for over wintering turtles and I am very pleased with the performance, and with the ease of cleaning it. Would buy another if needed.