Add a link to it on your email signature and your signature on other forums you use.
Post a link on website that are RELEVANT to this forum.,
Try to do link exchanges to build page rank.
CHANGE THE TITLE CODE FOR THE FORUM PAGES! It's curently Post Reply - walking forum... google isn;t going to like that!
Get a mention of it in trail mag or other outdoors mags...
Put a notice up at your local coldge, climbing wall, walking club!
Put a sticker / sign in your car?
Theres load of ways! Get thinking!