I will say this as well: if you don't have a net for your back yard and you're a serious disc golfer, you're missing out.
One of our facilities to train golfers at is an indoor facility, and we not only improved our own games over the winter hitting balls indoors into a net 30 feet away more than any previous time (including summer), the games of our students improved quite a bit more than normal as well.
Hitting into a net lets you focus on the mechanics and make appropriate changes. If you are fixing or working on the right thing, the ball (or disc in this case) will fly properly.
You can set up a camera, record yourself from a consistent angle, and concentrate on improving the form until you see changes, and if you're doing the RIGHT changes, you'll know the throws will improve when you get a chance to throw outdoors.
But indoors, since you can't see the flight, it lets you WORK on the mechanics and improve them the FASTEST, because you're not distracted by hitting a few funny shots (throwing a few errant discs).