If it is a bird species problem you can handle it as if you were keeping birds out of a garden. You can place a few dollar pinwheels around it or some aluminum pie plates on strings. Anything giving off flash and constant movement will keep the birds away.
If it is a rodent problem, go to your nearest Tractor Supply or Southern States and they should have deterants that can be poured or sprinkled around your pond that will keep them away.
Good Luck!