I keep my D-17's loader up with a 4x4 across the bracing that goes around the hood. That let's us work on it all we want, especially when we need to test the hydraulics and such. It's common enough that I'm surprised I haven't made a permanent 'holder' on the cylinders like the new tractors have.
I'm kinda with NIWolfman on the 'detach' and work on it side. Safest thing you could do is to make a loader working rack. It looks something like a super sturdy ladder that is self standing. You lift the loader bucket to the level on the ladder you need and pull forward, resting the bucket on the 'rung' of the stand. Then you can work on whatever and the bucket won't drop. When not in use it makes for a handy stand to clean rugs, hang things on, etc. A couple of 8' 4x4's with 2x4's for rungs would work.