Hiya
There is a way of stopping people from seeing your wall - and you can check what they can see on your profile, too. If you go into "settings - privacy settings" at the top of your profile page, on the right hand side, and go onto "News Feed and Wall" you can double check that nothing is ticked so when you post on someone's page, it won't show up in your news feed, which will help.
In "Profile" on the Privacy Settings, you can individually allow/unallow people to see whatever you want. i.e. stop someone from seeing your wall altogether but allowing them to see your photos , status etc. by customising your profile. Then check it by typing in the person's name in the same part of the site, and it will show how that person views your profile.
Hope that helps! I have lists for different people (restricted , private, only friends, only certain friends, only family) etc. and although it can be really time consuming, it does do the trick.