Squirrel Wars! (wait, wrong forum :-)). And I actually won't be complaining about squirrels until fall, when they start burying hickory nuts in my pots.
Ironically, I have always had the opposite problem with "permanent" ink on plant labels. It fades to illegibility after a year or two. I now use graphite pencil exclusively (we call them #2 pencils in the states), and the writing lasts for years (seven years and still going strong on the last go-round).
Since I also leave my labels in too long (see above) I do the following:
I write my plant ID code at the top of the label (so it sits above the surface of the soil) and I write it again about half way down (so that it's buried in the soil). There have been too many occasions when the labels have broken off and the top has disappeared (one is too many), and the back-up below saves the plant's identify.
I buy all of my labels online. I buy high-quality white labels for the ID, and thinner (and cheaper) colored labels for my collection status (red label: mother plant, yellow label: back-up, green label: extra free to trade, give away, etc.).