If you block somebody, if they are logged in they can not see your profile.
However, if they are not logged in then it is still visible to them, but since Matt changed the site so that you can only click on 1 or 2 pages before being prompted to log in, this should not be an issue.
If you are having difficulty with another member then plese do report it to us, we may be able to help
I blocked my friend on here, just to see if it worked a little while ago, as he had similar concerns. He couldn't see me at all whilst logged in. It's a good tool and works for anyone logged in... So they can't message you at all. I've unblocked him again now haha, although it was tempting not too lol.. only joking