Here are some notes from IRF<A href='http://www.irf.com/technical-info/appnotes/an-936.pdf' Target=_Blank>External Web Link</a>
For heavy work don't rely on the internal diode alone, use a 1N4004 or 1N5408 or heavy duty (TO-220 package) high speed diode.
A few cents to a dollar or two on a diode could save you 5 to 10 bucks replacing a dead MOSFET.