You can easily implement "Membership" or your forum, which means you control who sees what appears on your forum, and not allow those in the "Anyone" or "Registered" groups to have access.
However, the fundamental that anyone publishing anything on the web has to come to come to terms with is that if it arrives on someone else's computer then it is available to them to do what they will with it.
If someone is determined to use your material for their own purposes then no amount of water marking, encrypting, or other copy protection measures will stop it. It just makes it a little more difficult for the casual or inexperienced user to extract the bits they want.
The best approach is probably to take the same approach that shareware authors do and regard it as free advertising. Encourage people to use your material, but ask that they fully credit the source, so that the honest will come to you will to pay for your work.
Volunteer Helper - but recommending that users move off the platform!
Once the admin for GregHelp now deleted.