This is going to sound like terrific overkill. However. . .
If you have a lot of stumps and brush and what-not. It may be close to being a lost cause. The guy who rotovated my last plot pulled a few cedars out as he was going, but I would not have expected him to do any more.
If you have any work requiring a bulldozer, or if your neighbor does think about some way to get a guy into that orchard for a half-hour to an hour. You're not looking to be thorough or pretty. You just want some bare ground on which to throw down seed. You're looking for a guy who's hungry, want's a no-brainer job on the cheap for cash, and likes being creative.
The reason I bring this up was that I had a bum situation in my yard at deer camp. There was room for a circular drive, but the last half of the circle was soupy. In wet weather, we were digging ruts. I needed a dozer for a couple of hours to grade, and lay down some gravel. I also needed a few other spots worked on. It took me two years to find the right guy in the right circumstance. For $70/hour he came in and did it. While he was there I burned an extra half-hour and had him roll out into a field and tear it up. The treads alone do a pretty good job of chopping things up. He won't even have to lower the blade to get done a lot of this.
Then I came back and spread 2 lbs of clover seed by hand-- made a nice little clover patch until the drought took it last year.
While I was getting my stuff done, my neighbor decides he needs a little stuff done, and has the guy come over and work over an acre of his ground. If you have a totally overgrown mess, you can also turn a dozer loose in it and have the guy just tear a few lanes through it. The amount of edge you can create in an hour is tremendous.
Okay, so it's been 2 years and you can't find a dozer guy and your wife does not like the idea of a basketball court in the backyard. Now what?
Know anyone with ATVs? 4x4? Dirt Bikes? Invite them in for a few weekends. I allowed some neighbors in one summer in 2004, and I'm still enjoying the trails they made through the woods. Just lay down the rules and let them know what you want and how you want it. Let them know this is just for little while, and eventually the ride will end, and they will have to exit to the left and go looking for fun elsewhere. After they're done laying waste to things, just come back after them and re-seed. I've used a mix of Ladino and yellow sweat clover. It may be that in a few years you'll have to repeat the process, but it's nearly a no-cost solution.