Hunter 22s have a self kick up rudder like what you describe. You might be able to find one of those to study or copy. It uses a
line and a cam to hold in position, and according to the owner reviews I've read some people have augmented that with a wooden dowel as sort of a shear pin to make it stiffer. I don't recall seeing any drawings but there is at least some discussion on
Hunter Owners.com for owners sailing production sailboats under the owner reviews section. If you get really serious about it, our Sea Scouts have one, I can probably go take a photo or two of it. It's a new boat to us so we don't yet have much experience with it; as yet nobody has run into anything so as to need it.