Richard -

The usual arrangement is that the engine is killed if the mower deck is lowered (to make the blades run) if you're not on the seat.

The engine is also killed if the deck is running anytime you put the shift lever in reverse.

To back up, you must be in the seat AND the deck must be raised to stop the blades.

Raising and lowering the deck doesn't really cause significant wear on the belts. It does cause significant wear and tear on the old farts driving the mower, which is probably Bobert's real complaint.

The main drive belt is the clutch and you just drop the tension and let it slip to shift gears. The mower deck belt slips when the deck is up, and the weight of the deck pulls the belt up tight when you lower the deck; but the "slippage wear" from engaging/disengaging the deck is small compared to the slippage due to torque fluctuations from moving through the grass in operation.

The belts wear out when you stall them in the tall wet stuff and make them slip under tension (they can smoke pretty quickly), and/or when you "mow over the deadfall" branches and rocks. I usually try to miss any of the junk that sticks up much above the grass, but the average mower does make a fairly decent wood chipper for anything (wooden) up to about a half-inch in diameter, if you don't mind replacing the blades occasionally when they wear down (or when you hit a really big log).

John