I used to buy 4-5 pairs of 501's (shrink to fit, of course) and gradually destroy them, one by one they'd get ruined for polite society and graduate to the "work pants" pile.
A few years ago I got some carhartt pants & overalls and let me tell you, I spent less on one pair than on a pair of Levis and they're so much tougher. The trick is to change pants before I go work.
My last Levis are now about halfway through their lifespans so I'll need to figure out what to do for non-hard-work pants next in a year or two I guess... my wife likes the fit of these pants, so I'll probably stick with them, though they're definitely not made out of the same material that they were 20-30 years ago.