If legal in your state, you may want to consider a muskrat float, or a colony trap if the pond banks are totally too steep (not likely) for you to work with. However, you should have access to the shoreline somewhere to make/create a set using either a #110, or better yet, in that case, a #1 or #1-1/2 long spring.
You can seek out the use areas and make mounds as John mentioned. Do not discount the use of a good muskrat lure in conjunction with bait at such a mound set. If you can physically make a mound on the bank, create a shallow water shelf in front of it to accommodate a long spring of choice. In addition to the mounds, you could make baited pocket sets, using either the #110's or long springs.
Personally, I would set the bank dens using a #110, staking and locating (elevation) it with a stick, using a door jamb wedge as Gary suggested, or better yet, use a stick of 4 ft lath through the eye in the spring. You will not need a wooden wedge then - just adjust in such a way that it will lock itself on to the stake wherever you set it using the trap ring for that purpose instead as shown below.


And, if you want to consider a muskrat float, here is a simple one you can make:

These should give you some ideas for options to catch muskrats in your pond.
Jonathan