Bob,
I have an idea to suggest.
On the Forum Page are the different categories;
Open, Pond Construction, Stocking a New Pond, Managing an Existing Pond, etc.
I would suggest a new category Advertisements.
A new paid advertisement would be posted... say 1 a day.
Previous advertisements would then be slid down the lists just like previous posts. (maybe a time limit of a couple months or so before being deleted.)
Then when a buyer is looking for a product he can go down the topic lists and find the ad topic he's looking for.
It is just a hunch that most people that come to the forum would look at the daily ad also.
Perhaps this idea would meet the goals of creating revenue through advertising and access to advertisers through the forum without being intrusive.
