A 3PL single tyne ripper/pipelayer should handle cutting through roots & breaking mounds that your box blade can then level.
Also rather than renting a dump trailer if there's at least a day's work, when you factor in the hire of the trailer + un/hitching & loading ..etc. if you have another "operator" I'd be more inclined to rent a self propelled mini off road dumper c.3-5T (there as easy as any ZTR mower to drive ) & should be around $300/day ( for speed I prefer the wheels than tracks, I've an 8WD Yanmar 2T "toy", it will climb mountains & cart @10mph all day), the link below details what I'm referring to & in the event there's none for hire locally by you might be able to negotiate hire of one nearby that's for sale:-.
http://www.machinerytrader.com/list...lx=Contains&CTRY=canada&SO=2&btnSearch=Search
I have similar issues with some of the ground I am renovating. I had a standard box blade and it didn't work very well for my projects either. I bought a 6' Dirt Dog rollover blade that allows me to use the shanks with the weight of the box on top of them without grading. The box weighs 800 Lbs. and it cuts through all but really large roots. If I hit boulders I dig them out with the bucket. I use my electrically powered dump trailer behind my pickup to haul the dirt and dump it. It is a slow process, but it works.
More good ideas, thanks! I'll look into both, just not sure whether I can rent an off-road dumper locally but I'll ask around. As for the rollover blade, I had looked at these prior to purchasing my BB last year with my tractor. I should have gone this route as it really seems to be a better tool for the job.