As another poster suggested, use your loader & blade to clear & level the perimeter you plan to mow.
- Since all you are wanting to do is is keep the perimeter mowed back, a zero turn mower would be my first choice. You able to weave in and out of the trees allowing you to handle the mowing in a fraction of the time. You will use a lot less fuel, wear & tear on your tractor, & save yourself hours of twisting around looking backwards while brush hogging. I have a 60" cut Gravely zero turn mower with a welded deck. I have used it to knock down many a grove of sumach - no problem. 1st pass with deck locked in high/transport - "Brush hog" position then drop it down to 3" for the 2nd pass & I am done. If your will be mowing it 2 - 3 times a year, you will be able to do it in one pass easy! My Gravely is 4 years old & going strong.
- While in the military, I was tasked to mow an over grown area on a weapons range that had up to 1" samplings. When I went to pick up the tractor with bush hog that was suppose to be on reserve, the only type of mower they hand left was a flail mower. I explained about the saplings & was told to take it or leave it. After mowing the approximately 3 acres the flail mower had lost about 75% of the teeth/"T" cutters. I would not use a flail mower for brush control.
- If you go with a brush hog & are concerned about skid-digs, just add guide/depth wheels. Again auctions & Craigs list have good used brush mowers for a fair price.