How to keep spammers away from your site?

Hi,
I keep getting this one spammer posting 10 or so listings perday on my site and it getting annoying that I can’t block him/her/it.

Is there anything I can do to bock a particular user / email from posting on my site?

I do have my site set up to approve the listings before they are published, but I constantly have to be in the look out for one particular spammer and have to keep deleting that user and all their content, but they just appear the following day again.

This user re-registers and uses the same name and email over and over again every day, it maybe a bot.

I already have re-Captcha Settings enabled for GeoDirectory Registration, GeoDirectory Add Listing, GeoDirectory Claim Listing, GeoDirectory Comments, GeoDirectory Send To Friend, GeoDirectory Send Inquiry but this spammer stills get through.

I have the latest version of everything.

Each time the spammer posts I go to “All Users” search for the user name and select ‘delete->Delete all content’, but i just appears next day with more listing.

I wish there was a way do bock this user.

Any ideas on what to do?