Probably the best method is electroshocking. The next best method would be using a large net and the aid of a few people to work it properly. However, it isn't a reliable method to survey large fish and some smaller species. The next step down is what I've done- fish the pond using many different methods, depths, and baits. If it's early spring try a minnow or nightcrawler pieces in deeper water. If the bass and other species are in the shallows warming up try working a spinner bait real slow. Mix it up and try various depths and baits to get as broad an overview of the different species as you can. Even if you do well fishing you'll still probably want to net various depths and shallows to get a better picture of the fingerling and forage numbers. Keep a record of the number of fish, sizes, and weights that you caught and you'll be on your way to drawing conclusions.