Not to be a smartarse, but why not just safety wire through the rollpin to keep it from coming out of the shaft?
Brent - good to be cautious but did you look at the rollpin stress? An 1/8 dia pin has a 2100 lb double shear strength. I believe the key however, is to make yourself comfortable with the strength of the components you are trusting your life to. Just trying to point out that rollpins are tuff little buggers...
If you feel the need, coiled roll pins have an even higher shear strength.