You cleaned up your searches last month. Google got new ones today.

You spent an afternoon blocking junk searches last month. Your ads are clean now, right? Not quite. Tomorrow someone will type a search nobody has ever typed before, and your ad can show for it.

Google itself says it sees billions of searches every day, and 15% of them are searches it has never seen before.

Source: Google, Understanding searches better than ever before

When your keywords are broad, Google decides which of those new searches "match" your ad. Some will be real buyers. Others will be:

• a question from a student
• a product you don't sell
• someone looking for a different brand

The fix: your negative keyword list (the words you tell Google never to show your ads for) is never finished. New junk arrives every week, so it needs a quick check every week.

The habit: once a week, open the list of searches that triggered your ads (Google calls it the search terms report). Sort it by cost. Look only at the searches you don't recognize, and block the clear junk.

One warning: check before you block. A strange new search can also be a new buyer.

If you'd like a second pair of eyes on yours, JunkTerms gives you a free analysis of your search terms file: junkterms.com/demo