I have had two ponds in the last 12 years. Both were over 25,000 gallons. In the first, I used submersible pumps. I housed them in mik crates loaded with rocks. They never clogged and that pond was loaded with plants etc.
Now I upgraded to an external sequence pump which, I thought would be a much better choice. It sits inside of a skimmer box. It clogs at the inlet as well as in its basket on average of once per day literally stopping the pump altogether. It is a royal hassle!
The veggie filter has a small submersible mag drive pump running water into it. It has a housing around it to keep the big stuff out and despite the fact that the housing is constantly covered with guck...it continues to run and pump water.

This sequence pump is driving me a bit nuts. Is it possible that the submersibles dont clog so badly?