If you want to track a buddy' s dog then check with them & make sure you get a box on the same frequency (216; 217; 219 etc). In my opinion & from my own personal experience the Wildlife trx 1000 is the best box on the market. Brand new it is $770, but worth every penny when you add up gas & time saved looking for dogs. This particular box covers the whole frequency range from 0-999 and will work with any brand collar on the same freq.
Good luck & Good Hunting!