Avast has its own self-defence module.
You can get programs in which you can password protect and or encrypt folders. But with that comes its own problem if you forget the password, etc. you could end up locking yourself out. For me this risk however small has stopped me going down the password/encryption route to protecting folders.
You should start by forcing all users of your PC to have to log-on and never leave your PC logged on if you leave it.
Why is it that you are even considering this ?