Not op, but a common tactic is to put honeypots in a page set to be forbidden in Robots.txt. Not respecting Robots.txt is making you a bad crawler. I have marginal blog, but its somewhat indexed and it gets tons of traffics from crawlers
I also explicitly tell all crawlers not to index the images on my site, actually, so I feel even better about serving the ones that do complete junk.
Not sure why I get more crawler traffic than I do legitimate traffic tbh - it's a relatively new website that I've been trying to sort out the SEO for as I'm trying to get photography work, so it's probably started cropping up on the radar of scrapers looking for training data.