If you are leaving your dog with friends, be sure to leave them tags with your friend’s number.  I was dog sitting for a friend once and his dog jumped my six foot fence and escaped in less than five minutes.  I then spent a panicked afternoon driving around the neighborhood looking for the dog because his collar had my friend’s phone number on it and I didn’t have keys to his house!
So do your dog and your friends a favor, and make sure your dog has a good phone number on his tag all the time!  This tip came from Wise Bread.  Here’s how they do it:

Interchangeable ID Tags. Our dogs have three sets
each. One set is for when we are home or in that general area. It has,
in addition to each pet’s name, the numbers for both the house and our
main cellular phone. The other set is for when we are traveling other
distances. It has our main cell number only. The third set is for when
they are with the sitters, which they are when we travel
internationally. It has their main house and cell numbers. We swap out
whenever we are changing situations.

Photo by This Year’s Love.