If you don't brand, the only other permanent form of I.D. is a tattoo in the ear.  And permanent i.d. is a must for any good record system.

'We' use Ritchie engravable tags and use a dremel to engrave them.  The tags themselves hold up real well even after 8-10 years, but the buttons used to put them in usually start failing about that time if not sooner.  It's not at all uncommon to find a good readable tag with a broken off button out in a cow track or under a tree, etc a couple of years after replacing that tag with a new one. 

We use small Duflex tags in calves, and then put the Ritchie tags in after weaning since those tags seem to be too heavy for small calves.

We tattoo everything on the place, except steers, at weaning.  If any tag disappears, read the tattoo, make a new tag and animal is id'd again until the next time a tag is lost.  Some cows are harder on tags than others, but most usually only get one tag cause if their tag lasts 10 years, they aren't far from leaving our herd anyway. 

Bulls seem to keep their tags until they get together with other bulls, then tags seem to take their leave.  Some bulls get new tags every year it seems.  One of these years, I think I'd like to start freeze branding.