I am late arriving, but let me see whether I can understand... a) you are pretty sure you aren't going to get rich off your work, but b) it would chap your buns if the college took your material, handed it over to a TA and had the TA teach subsequent sessions of the course. Is that right?
If that's right then the question (in the United States) boils down to whether what you've produced is a "work made for hire." If it is, it belongs to the institution; if not, it belongs to you.
Getting a standard contract modified, particularly if this is a state institution, may be nearly impossible. I think I'd write a letter to whoever signs the contract saying something like, "My understanding of our contract of _____ is that all rights to the course material which I may develop to deliver this course vest in me, and that the University of _____ claims no right to any intellectual property developed in the preparation or conduct of this course. Please confirm that my understanding is correct." Then get a letter signed by whoever signed the contract that essentially repeats your question as a statement. It will probably be easier to get this going with a personal meeting than with an exchange of mail.
Then put copyright notices on everything. You might also want to record your lectures: http://bbrown.spsu.edu/papers/podcasting/podcasting_protects_ip.html
(I am not a lawyer, and this isn't legal advice. If you think the materials are worth tens of thousands of dollars, you need an IP lawyer.)
Edited to add: Take note of MarkJ's commentanswer here and consider putting all your stuff on a personal web page with copyright notices attached. I've used the Creative Commons licenses for my own stuff. Publishing it that way won't keep others from using it, but will preserve your claim to authorship.