How can I prevent link submissions from sites that are unrelated to the topic of my site?

While you cannot specify which topics to allow link submissions related to, you can choose specific words that will cause a site to be filtered out automatically. Under Change Settings, Link Approval Settings, you can enter any number of words or phrases in the Content Filter field (one word or phrase per line). When a site is submitted to you, either through your site's link submission form or as an InstantLink invitation, that site is checked against the content filter. If one of the words or phrases you entered is found, the site will automatically be rejected. This is useful if you receive many link submissions for sites that deal with topics unrelated to your own site's topic.

If you are receiving many irrelevant submissions from one particular webmaster, you could enter that webmaster's e-mail address in the content filter. That will prevent any submissions of sites that use that e-mail address.

When you do receive unwanted link submissions, it is much faster to delete them all at once rather than one at a time. If you're not sure how to delete multiple links at one time, you can find out here.

In addition to filtering out link submissions by topic as described here, there are other ways to automatically filter out low quality link submissions. These are described here.

If you're wondering how to prevent sites from exchanging InstantLinks with your site automatically, so that instead each InstantLink invitation will require your approval before the exchange is be made, that is described here.