How would you like to save 20 percent on your lodging bill the next time you visit Yellowstone National Park? It's really quite easy, and you can earn a tax deduction in the process.

All you need do is join the Yellowstone Association Institute, the non-profit group that offers a wide range of field seminars in the park throughout the year.

Of course, there is a catch, but it's a somewhat small one: the 20 percent off Xanterra Parks & Resorts is offering Yellowstone Association members is good only during May and October this year. While May weather in Yellowstone can definitely be so-so -- snowy and rainy and muddy, with breaks of incredible gorgeous weather -- early October weather often can be outstanding, with daytime highs in the 50s and even 60s followed by nights below freezing.

Plus, fall is when wildlife are highly visible, as elk are in the rut and coming down to lower elevations, and wolves are following them. Bison, of course, are visible any time of year in the park.

A membership in the Yellowstone Association can be had for as little as $35 for a year. With lodging rates running $96 a night at the Old Faithful Inn in May and up to $145 a night in October, a two-nights' stay will earn you back your Yellowstone Association membership fee, which, of course, is tax deductible.