I bought the famous Harbor Freight demo hammer & used it one day setting the second course of logs.
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=93853

Unfortunately the logs we used weren't large enough to easily stand on/balance & use the demo hammer on the rebar, so needless to say I swung the sledge alot.
Demo hammer looks & runs like new. Have box & instructions
Also have a nice ground rod driving bit (SDS-max) that was not all that cheap ($50+)...

Sold!

Thanks