How many times have you headed off on a national park trip and conveniently forgotten your Passport to Your National Parks? Have you ever run out of space for cancellations more quickly than you would have thought? Or, has your Passport gotten dog-eared from being stuffed into your back pocket or pack?

Well, the folks at Eastern National have tackled those problems while celebrating the Passport's 25th anniversary.

Since it debuted in 1986, the Passport has been a highly convenient and inexpensive way to track your national park visits. Once you've paid for the Passport ($8.95), that's pretty much it. Cancellations that denote the park you're visiting and the date of that visit are free to be had in park visitor centers. Regional stamps, if you want to add them to your Passport, are 50 cents a piece, or you can buy entire collections for $3.95.

But the ease of misplacing the 3-and-a-half inch by 6-inch, spiral-bound Passport long has dogged me. I have at least three, although I can only locate two.

To overcome that problem, Eastern National has created a 25th Anniversary Explorer Edition ($49.95) weatherproof portfolio that features larger (4-and-three-quarter inches by 7-and-three-quarter inches) park pages. This binder also features several pockets into which you can stick things such as your annual parks pass, pens or pencils, flashcards for your camera, even maps. And the whole thing zips closed, so if you remember to zip it nothing will fall out.

And, for those who visit quite a few parks each year, you can order a 36-page expansion pack ($6.95) that features "20 pages for national park cancellations, 10 pages for national park cancellations and regional stamps, and six pages for National Stamps and commemorative cancellations."

This expansion pack, the folks at Eastern National say, can handle nearly 400 park cancellations. If you visit lots of parks, and tend to misplace the smaller Passports, this is a great way to go.

But if you don't think you need to go that route, the 25th anniversary edition of the regular spiral-bound Passport offers 12 additional pages for cancellations, versus four in the previous edition.

Both versions continue to divide the National Park System into nine regions, and there are short bios, including contact information, on each unit in the regions. Each region opens with a checklist page so you can quickly recall which parks you've visited. These checklist pages also fold out to reveal a map of the region with the locations of the various parks clearly noted.

If you're well-familiar with the park system, you might notice that the Explorer Edition in its introduction refers to 391 units, not the 394 that currently exist. That is simply the result of the time it takes to print this information, the fact that it can at times take a little while for new units to get up to full operations, and for the appropriate stamps to be created. And with Congress somewhat regularly ordering the Park Service to consider adding new units, it makes sense not to rush out a new edition every time a single unit is added.

The folks at Eastern National tell me that the Passports are viewed as "organic documents" that continue to evolve and are updated with each successive edition.

While Eastern National might be best known for its Passports, the non-profit cooperating association has been generating educational and interpretive materials for national parks since rangers from Gettysburg National Military Park formed the operation in 1947. These days Eastern National produces materials for more than 150 units of the National Park System.