Please don't think that an identification tag is all you need to keep your pet safe should he or she ever get away. Collars and tags can fall off, can be taken off, can wear out, and can be modified. There is certainly nothing permanent about them. Microchips, on the other hand, are absolutely permanent, are immutable, and are extremely safe.
If your pet is not currently microchipped, I highly recommend having it done as soon as possible-that chip might just save its life!