I put 150 yds of 30# braid on my Quantum catalyst.

i have never had braid slip on the spool........nor have i ever heard of it slipping.

with that being said, i would recommend if you are chasing big fish to have a few yards of 10 lb mono attached to the spool bc if you get spooled by a big fish you dont want to be attached to that rod with 50+ lb braid. you need something that will break fairly easy.

Good idea.

1 thin piece (1/2" wide)of sports tape is the answer.
grips the spool, grips the line, no mess, and doesn't take up spool capacity. do that, and a regular slip knot reversed to the rotation of the spool. simple yet effective. Remember what IGS said about tightness, If you're not sweating when you're done, it's not tight enough. I normally load my spinners w/ about
5-6# of drag.
As far as capacity, yesterday I spooled up my cabo 40 w/
30# suffix & nearly emptied a 300y spool. Thinking around
200-220 y. Probably never gonna need that much, but the idea is to fill the spool. Maximum casting distance and minimum line issues can only be acheived w/ a full spool, meaning fill to
1/4" of the lip of the spool.

I beg to differ. this is fishing, the idea is to catch, not break them off w/ 150y of braid hanging out of their mouth.
you dont need weaker backing, you need MORE DRAG!
More to the point of not using mono, you will have more cap. and being spooled is out of the equation. This is where good equipment makes or breaks the deal.