All I can say is if you have a mud bottom pond, there is absolutely no way to keep wildlife out without totally enclosing it in a conservatory,
with a poured cement surface all around it and up past the edges of the greenhouse foundation.
People,
everyone here, should just accept the wildlife a pond attracts, including the predators and deal with it.
If you're not able to deal with it, don't have a pond. It's that simple.
So what works for me, is planting the pond, stepping back and watching mother nature do her thing.
Large lilies go in deeper water up to 4-5 feet deep, smaller lilies go in the shallows.
Don't know how a plant grows, what it likes? Google it and find out.
If a muskrat comes, pray to the 'birds of prey' goddesses and gods.
I do occasionally 'ping' blue herons and egrets with an air pistol, but not to kill or harm, just at the loose tail feathers for a sting,
and never let 'em know where the ping is coming from. In other words...don't let them associates seeing you with getting a ping.
They've gotta learn to associate being at the pond with getting a ping. Then they'll stop coming.
Here's an article I was asked to write for WGI...
http://www.watergardenersinternational.org/journal/1-4/joyce/page1.html