With most PK rings there is always the likelyhood that the coating will wear off after time, this is down to the way they're made. Murphy's Magic bought the rights to the Wizard Rings and redeveloped them, calling them "Kinetic" rings. They come in a number of styles now and seem to be the best quality ones that are easily accessible. They're not too expensive.
If you REALLY wanted to ensure the highest quality and something that will last for a long time, you could go and have it coated in gold yourself; it'll cost a bit, but lengthen the lifespan. For the cost of replacing the ring however, I wouldn't bother going to those lengths, you could be a bunch for the same price!