800gal pond is too small for even koi, let alone a tiger muskie in the long term. Generally speaking, for fish which grow to 12inches or more, the tank/pond should be at least 4 times the maximum length of the fish to find the length, and to find the right width of the tank/pond, it should be 2 times the adult maximum length of the fish.
I'm no expert on these fish, but i've heard they'll grow to 3ft+ in 4-5 years time, so an 800gal pond may surfice for a while, but are you really going to want to upgrade the pond in the near future? Lengthening/widening ponds isn't easy work. It will probably be best to avoid this beast of a fish if you don't see yourself giving it a much larger pond in the future.