Originally Posted by Borrego Dave
The joke saying around the shops yard was "stop when you hear glass"
Along with that, "If you hear scraping, and feel increased resistance, more gas is NOT the answer".
Learned after 30 years of driving and backing ambulances into unfamiliar, often dark driveways as a paramedic. Not by my own experience, mind you, but I did see it demonstrated - big bill to repair both the ambulance AND the steel fence.