My neighbor asked me to bush hog his overgrown field (once a hay field) next to mine. I just got the bush hog in April and am still learning about it. It has already hit a rock the size of a softball out the back 3-4' in the air at a good clip. The horses had been in the lower part of the pasture (I was in the upper) but took off for the barn when it came out with all of the noise.
I am using an older 5' International Agitech tow along bush hog. (hitches to the drawbar and two wheels trailing. I set the front lower than the back. I usually run along with the bucket on my TC30 maybe 10" above the ground. I go right over saplings, thorn bushes, apple trees, dogwood, birch, spruce, white pine up to 2 inches or so, 3" sometimes. There's noise, wood slivers- sometimes the root ball and bit of trunk. I travel at mid range 2nd at about 1800 rpms. 3rd is too fast, 1st too slow.
One patch of birch was awfully noisy and almost stalled the tractor- clutched it in time. I thought - that's the last time I hit a birch, but on my swing by again- I saw I had run over a pile of rocks and the birch had simply grown in the middle of them.
I enjoy it and it preserves the fields. Everything else up here goes to trees in no time.
I keep our pasture low for my wife to ride on, and slowly the weeds are being replaced by grasses.