Actually, as I understand, your transmission IS designed to hold your car, even on a pretty steep hill. Perhaps you shifted into park errantly while still moving at some point? Or perhaps your shift lever isn't adjusted properly (and that's just a guess)

__________________
"If God had meant for us to walk, why did he give us feet that fit car pedals?" Sir Sterling Moss

Michael
2014 E63S Estate
2006 SLK55
1995 E500
1986 Porsche 944 turbo