I've never caught doggies so I'm happy to stand corrected but thought doggies had conical type teeth rather than cutting teeth. From watching the JM jigging vid from Chesterfield it looked like they weren't getting bitten off by doggies- mostly busted off on the bottom I think.
My thoughts were that if you did hook something very large with with sharp teeth (shark) you would probably want them to bite the assist off rather than losing it all by using a steel assist.
Just a theory.

Zylon is a lot tougher than standard Kevlar.

I would suggest heat shrinking over the steel assist cord and hook. This provides a stiffer rig which I think is better. Also steel rigs tend to put fish off, the plastic heat shrink is a bit better in this regard.

X2 for Zylon

Thanks for the input. I'll try some heat shrink. The yellow cord is the owner 150lb Steel cored line.

Last year the guys were Getting bitten off using 400lb zylon hence some wire this year.