Blocking Guest Account on Mac

Hey guys,

I have a number of filters on my phone and Mac as well as accountability software, however I have come across a loophole which has played a part in a recent relapse. My macbook has the option to open a guest user, which only has safari browsing and does not allow installation of any software, nor does it store data after each use.

Does anyone know of a way to disable this or similar?

Thanks in advance!