A little over priced, but I use the Massey 4' tiller on my GC2300. I have two seasons on it and it is great.
I can cut a 30 x 50 garden into a lawn in an hour - inluding working it about 10 inches deep and turning in any mulch products you happen to have.
Rocks have been no problem - spits them right out with no damage. The tiller is built for a more powerful tractor than mine - so you are not going to hurt the tiller. It does have a clutch for safety.
If you are only doing light duty tilling, check out Tractor Supply - they have one that is 1n the $900 bracket. I paid about $1500 for mine. But, like I said - it won't break.