I am assuming that you only have 4-5 per trailer load? Make 4-5 sleds out of 4x4's and plywood. Chamfer the leading edge of the runners (4x4's). You will need three 4x4's - two on the edges and one in the middle. Bolt a ring into the middle one on the side with the chamfer. Load them on the trailer with the ring side to the back of the trailer. When you get home, chain the ring to the loader bucket or better, the draw bar and drag them off the trailer. The sled will traverse pretty easily. If you put steel or plywood on the bottom, they will drag slicker than deer guts on a door knob. You have to chamfer the plywood too.
You can also make a single stone sled. Basically that is 2 pieces of pretty thick steel plate (bigger than the stone!) that are hinged in the back. The front of each 1/2 has a ring. A chain or cable loops thru the ring. You place the open "sled" behind the stone you want to move, hook the chain or cable to the tractor draw bar. As the tractor moves forward, the two open sides are drawn forward and together until they go under the stone and clap shut. Once shut, it drags with relatively little effort. You have to beef it up to take the abuse - use good metal working methods as needed.
jb