Adding captchas to any website is trivial thing and if I remember correctly I saw several scam services that used them in past, so this won't protect you from anything.
To support Captcha, it is necessary to activate JavaScript in browsing, which leads to the leakage of some data. This was the way in which the location of the founder of the Silk Road was discovered.
Is there an easy way to remember that site, maybe @Chipmixer should buy/add a domain/sub that redirects the Onion address or create something that makes the address recognizable.