Don't know what part of Texas you're in but sounds like West of 35.
The Lone Star GSP Club will be holding a snake proofing clinic on 08/04/2007. Info is on their site
www.lsgspc.org

We've taken our dogs to these clinics for years. Get to start with the new pup this year, poor baby he's gonna hate it but I'll feel better about taking him out once he gets a bit of an education on these demons. They do a great job. If you can't make it you might try to find a local bird dog trainer. Many times they'll hold one of these sessions, usually before dove/quail season when most of these instances occur.

If you need to find someone closer to home let me know. Might be able to direct you.