Several things to try
I was also a little confused the first time I read your question. I wrote a response, but then deleted it without sending it. What I recommend you do, since you already put Liquid Wrench on the bolt that the rudder pivots on, is take an adjustable wrench and put it onto the locking handle, which will in effect, make a longer handle. I would do this with the rudder off the boat, and possibly on soft grass, or carpet. Then loosen the handle. I have had the bolt SNAP on my mine, so I recommend that once you get yours loose, you replace the stainless steel bolt. Make sure that it is a high strength bolt. (It will have lines on the head of the bolt to show that it is high strength). If the bolt breaks, it could be disasterous under the right conditions. Once you get the rudder locking handle loose, the rudder should swing up easily. (Mine actually swings up too easily, and I have to put a pin through it to keep it from coming up just from the drag created by the boat moving through the water. The pin that I use is made from nylon, and that is important. I don't recommend a harder, stronger shear pin.) The little leaf spring that snaps onto one of the gudgeons, did not offer enough resistance to keep the rudder from popping out on my boat either. What I did was bend it out more than it was originally bent. Now when I snap the rudder into the gudgeons, it really snaps in. I have not had my rudder snap out since I did this, and I have had it hit the bottom a few times. The idea of tying the rudder onto the boat, does sound like a good one to me. I just added it to my winter list. Aldo