Marking wood duck houses with date???

[BLACKJACK]

I make a few wood duck and bluebird houses every year (out of cedar or cottonwood) and I like to mark them with the date on the bottom, just to see how long they'll last. I've been using a soldering gun and kind of etching into the bottom the date like '98' or '07' but I've found that as the wood weathers and ages and darkens, its really hard to read that date.

Any better tools for marking wood with a date???

Thanks.

[sparcebag]

Try roofing nails on the bottom,make a code like 1 nail is 08 -2 nails 09,Just keep a code book, if your like me I'd forget the code in the first year.

[IFallsRon]

Make a metal tag and get the Operation ID tool from your local cop shop to engrave the information.

[Jeremy airjer W]

Use a Dremel tool and carve it into the bottom?