|There's really only one way to do this humanely, and that's with fencing. You can live trap the critters, but then you need to find a place to "relocate" them, and they can be quite dangerous to handle.
To build a woodchuck fence, use strong but bendable mesh fencing and metal posts. Build a fence that stands 3 feet tall, with the following modifications to increase its effectiveness: If possible, use a 6-foot wide mesh, and bend 12 to 18" outward slightly at the bottom, then bury this in the soil. Attach the above-ground portion to the stakes to a height of about 3", then let the remainer--1 1/2 - 2 feet--extend above the posts and bend it outward as well. When the woodchuck attempts to climb over it, he'll find himself upside down and just flop back because he's so heavy!