I added FOPS (falling object protection) and limb risers to my NH TC33D a few years ago. I did not do the work myself, a local 1-man fabricating and welding shop did it. He's done a number of forstry mods for larger tractors, and I was impressed with the thought he put in to it.
Detail of the attach points to the ROPS. There were 3 holes in the ROPS already. Two of them were used to attach the FOPS structure. (You can see the third in the middle in one of the pictures.) If you don't have the three holes already, and want to avoid drilling your ROPS, you could extend the two "C" shaped pieces back a bit and run the bolt down behind the ROPS bar, so it clamps to the ROPS, rather than bolting to it.
If I were trying to design to protect from heavier objects, I'd add some upright posts going from the loader attach points up to the front of the canopy. Since I'm mostly trying to protect from falling branches (not falling trees), this seems plenty strong enough.
Things I would do differently:
Since my loader frame is on full time (I either have the bucket or the grapple on all the time), I would probably extend the front of the limb riser straight up for about 1 foot before it starts angling back up to the canopy. It works fine as it is, but moving it up to just below the height of the loader arms would give a shallower slope. The lower part as it is never hits any limbs anyway, since the loader arms stick up higher. If I regularly operated with the loader frame removed, I might only raise it up 6" or so.
I covered the top with expanded metal, since I figured I would want to see what's above me, and I wasn't really concerned about shade. If I were doing it over, I'd make it solid. It's no fun when I drive under some cedar branches and all the small pieces fall through the expanded metal and seem to get everywhere (mostly down inside my shirt). I'll get around to switching this at some point.
