Jim:

I also saw the incident Edgar mentioned above, I would suggest that you make an opening on the bottom of the rudder near the leading edge and insert and glue with Hysol a block of hardwood shaped to fit the inside of the rudder flush with the outer skin and flush with the bottom of the rudder, and wide/long enough to have enough meat for the horn to grab to, also use a carbon or G-10 horn, not a FRP horn which is what our friend had when his failed, I have encountered that same problem as you with models in the past, this solution has worked perfectly