I saw this ad on ebay and I'm tempted:
http://www.ebay.com/itm/Air-knife-c..._DefaultDomain_0&hash=item2ec338090aThose things are like $1200 a pop. To make it easy to dig up lines. I am not sure I want to add the price of compressor rental to estimates. It sure as hell would make digging hard ground easier.
Anybody have experience with these?