The biggest deterent to cheating is the lack of incentive. The best time I had calling in a contest was last year. My wife and I took third place and won $36. With a small pot (i.e. low entry fees), there is little real motivation to cheat. I know it's not as "cool" as winning a grand or a new rifle, but in this situation it sure made for better friendly competition and fun.
Basing the winnings on weight also has some merit, but many will argue that method has as much to do with luck and access to good habitat as it does with skillful calling.
