We just got a new puppy and I'm planning to get a GPS collar for him and our other dog so I don't have to keep them leashed while hiking around. He'll be about 40lbs probably, the other is ~28lbs right now. I've not used GPS collars before, most likely they'll be used for less than 6 hours at a time and within 160 acres area, fairly heavy brush in most spots. I'd appreciate any advice or experience.