I use my own fork of BellaBuffs, a PHP script, to build my fanlistings. BellaBuffs itself has an isBot() function for detecting bots, which is then used in the fanlisting’s submission forms to block bots.
However, I still got spam submissions from my fanlisting forms, so I ended up adding the option to enable security questions in my BellaBuffs fork. In my own fanlistings, my security questions are simple maths questions, which do help to reduce spam submissions a lot.