I had the same problem, particularly when powering in reverse if you forget to really grab the tiller. I bought the PowerThruster from this site, a bit pricey but easier than fashioning your own guard plate. I was not interested in the extra thrust claimed, but just as a way of keeping rudder from blades. It works for that. The outboard does of course prevent 100% rudder swing, but on my H23 that is not an issue - it has plenty, even up against the outboard, when motoring.