How about adding a CAPTCHA to the search form that the user must complete before performing the search? Or if CAPTCHA is not received well (I know the Google reCAPTCHA has been overly stringent lately), maybe try other security questions like asking "What is 2 + 2?", "Type in the second/third/fourth word in the following sentence" etc.
I use Google to search TG, so either way it's no huge deal for me