Yeah just ignore robots.txt because there's others solution.

If the site don't want to be scanned they can adopt a lot of counter measure and robots.txt will not save it from abuse.

He remind me the old days when my website wasn't working from US because I just fake that the site was down because there's no reason that somebody goes to my site from US (I know it's kind stupid, but when all your content is in french and you are a kid... :) )