I once used a weight like Herb mentioned and flew a couple hundred flights on the plane in a couple of seasons without any problems. The weight was fairly precisely fitted to the propshaft and keyed so the prop actually interlocked with the weight.

Later on I read in RCM that it was dangerous so I took the weight off, but my experience was that it worked for me. Maybe there was more than one manufacturer out there and I got the good one.

Your mileage may vary.