Pollute your site with nonsense that’s invisible to users. Things like pages that are linked to with invisible links that are just walls and walls of random text.
Good idea. I will made a invisible link to "traps for bots". One trap will show random text, one will be redirect loop and one would be random link generator that will link to itself. I will also make every response randomly slow, for example 0,5 to 1,5 seconds.
Good thing is that I can also block search engine crawlers from accessing only the traps.
OP still wants search indexing, in which case it's a big no-no - it can be perceived as spam by search engines, and links your pages to tons of unrelated keywords.