How can you stop your fountain pump from blocking every few hours?

How can you stop your fountain pump from blocking every few hours?
We have bought a new pump for our pond. Its not a fish pond, just a water feature. The fountain display gets poor after a few hours because bits of grass and soil keep getting blocked on the holes on the fountain head and I have to keep unplugging the pump to clean the fountain head. Is there something I'm not doing right?
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Pumping Environmental Services, Colorado