All dogs that are treated well will be good protectors.You want big dogs means like Labs, German Shepherds, Doberman Pinschers, etc. or any mixed breed dogs will do as well.
I looked up the dates for LGRA in August in Oberlin and I will on vacation that week in NC. I would like to meet up with you for a play date one weekend. Cody gets his staples out on Tues. (yeah) So after that I would be free most weekends until Aug 20. If you have suggestions on dog parks to go to let me know.
