You want an intelligent dog with a work ethic, and bigger is better. Herding breeds that also guard are the best choice. Watch out for purebreds bc the genetics are producing scads of dogs with genetic physical problems, and you want a healthy specimin.
My dog, "Xena" (1998-2008, RIP), a GS/Collie cross was a very good choice.
After owning a BC cross ("Rose," b. 2007, Husky/GSxBC) I like this, too. Rose is TOO brave for her average height but 60 lb frame. She runs a minimum of 2 miles/day--we know bc we put a pedometer on her--but it's mostly playtime with her friend, "Pygma", and scouting the property for rabbits. She barked for 45 minutes at the coyotes one night when she and I were sleeping in the tent by ourselves (and the horses) and there was a large company of coyotes in the park (at a CW event.) When we ride our north 3 acres, the dogs come along with us, and I like that, too.
Here are the dogs:
Xena, 1998-2008, RIP
Rose, 5yo Husky/GSxBC
Pygma, 4 1/2yo Lab/GSxPitbull (good watchdog, poor guarding dog, but GREAT Velcro dog)
Rose and Pyg "Wolfing"
Rose & Pyg Tandem Chicken work