Very nice design.
I took a 10 second look and saw a few on-page SEO tweaks that could be done, but nothing major.
The most glaring was your URL design could be improved a bit to add the word "metal" into the various keyword strings.
For example, on
Beach and Underwater Metal Detectors, your URL is formatted like this.
http://www.woodlanddetectors.com/category/58-beach-underwater-detectors.aspx
It should read like this
http://www.woodlanddetectors.com/category/58-beach-underwater-metal-detectors.aspx
Three big on-page SEO arbiters are title, domain and intro text. If you're missing a critical keyword here, it won't help capture the exact match search string boost for the most desirable terms. To give you an idea of the difference in prospective search volume:
Google is smart enough to recognize the semantic relationship of the text, but it does boost strongly for on-page factors that exactly match the search string, without going overboard and getting spammy.
Same thing with something like Fisher.
http://www.woodlanddetectors.com/manufacturer/7-fisher.aspx
Google reads that as "Fisher (via Title and URL)" + "Detectors" (via keywords in the domain) but will only presume a semantic relation when people search for "Fisher Metal Detectors" as opposed to giving you a relevancy boost if you had that text in the title and URL.
I also don't seen an address- it does not inspire trust for new customers who may be unaware of whatever reputation you've earned. That alone will turn back a lot of consumers. I worked for an upstart .com some years back who also made this mistake- upon correcting it (and in a big way, prominently featuring their address at the bottom of every page), their sales jumped 15% in one month. It was pretty remarkable.
