For years, I've just grabbed a brick, a board or whatever to shim up one leg of my extension ladder on uneven ground. PITA, and prone to slippage. Finally bit the bullet and bought this. Handy as hell and solid. Even has a hole on each side of the foot you can drive a 16D nail through for extra insurance. Spent today using it, and man, what a difference.

Levelok LL-STB-2QC Ladder Accessories, Chrome + Free Shipping
Levelok LL-STB-2QC Ladder Accessories, Chrome + Free Shipping
www.amazon.com