We just use a sledge. We've got a couple of sizes -- 6lb with a 24" handle for lighter duty and 10lb for those stubborn timbers. You have to use pads to protect what you're hitting.

The split head mallets (Garland makes a good one) with rawhide faces are awesome for moving timbers -- even a 4 pounder will move a lot. You can hit oak without a pad. They also drive a chisel like nothing else.

I wouldn't recommend making a persuader out of a hard wood -- it will really bruise what you're using it on. (learned the hard way)

Also we made one once that must have weighed 25 or 30 lbs -- way excessive. Needless to say it didn't get used often.

Jim Rogers wrote an article for the Guild Journal a few years back on making commaders -- if you have the dvd of back issues you could search for it.