Zebra muscles are definitely tough on spinner rigs. Making sure that you have the right line for the job is very important. You asked about fluorocarbon as an alternative to XT and I would say that it could be a good choice but the important thing is to up the size of your line from 14lb to 17lb or even 20lb test. And be careful to keep the line wet as you tighten down your knots with fluorocarbon lines. If they get hot from friction in the knot tying process they can break down easily.
Another option for tying spinner rigs for the Zebra Muscle challenge is to use Berkley’s new IronSilk line. this line is extremely abrasion resistant and stands up better to the zebra muscles than most other lines. Same thing here though, go heavier with your line. 17lb test is pretty common in my boat.