Our dogs' tags were forever breaking or wearing so badly that they became unreadable. Plus, they were so small sometimes that the engraving was microscopic. Did you ever try to read the tag on a wiggly stray puppy? It's almost impossible without removing the tag first.
That's when I discovered embossed metal tags, just like military "dog tags." They're strong, big enough for plenty of pertinent information, and resistant to wear. This is the last dog tag you'll ever have to buy for your pooch.
They're cheap, too. About $5, which includes shipping. They arrive fast, and their service is excellent. Here's the website I use: http://www.pet-tags-online.com/
There are others doing the same thing, but this one has been foolproof for years.