I have a gravel driveway going horizontally across a hill, and have trouble keeping the gravel in the driveway, especially during snow. This is because every time I shovel out the driveway, stones get picked up by the shovel and thrown into the grass. Of course, this takes a long time to pick up. Big rainstorms also wash out gravel. It is crushed limestone in the 1/2-1" diameter range. I can't pave it because I haven't got the money, and there are some nice trees over it Which would be bothered by pavement. How do I keep gravel where it belongs?
Two traditional methods which work but may not agree with you are:
1) tar the surface. I believe you could get a local construction company to do this as spraying hot tar may not be a chore you want to do
2) If your driveway is already compacted and drains well this is my preferred solution:
Crusher run or Crushed stone: this is generally limestone or dolomite that has been crushed and graded by screens to certain size classes. It is widely used in concrete and as a surfacing for roads and driveways, sometimes with tar applied over it. ... A special type of limestone crushed stone is dense grade aggregate, or DGA, also known as crusher run, or colloquially as "crush and run". This is a mixed grade of mostly small crushed stone in a matrix of crushed limestone powder.
This should be available in bulk at good prices from any quarry or landscape supplier. Spread in a layer so the top of the existing gravel and compact with a roller and apply water to harden. For spots where it could wash out mix with Portland cement.
*1 cu. Yd. will cover approximately 100 sq. ft. at 2" deep
If you are going to go to the effort of doing this you should also do some grading on the uphill side to add a ditch and add piping to let the water through from one side to another.