If you keep breaking off use heavier line. If you are breaking with 6, use 8. If 8 is breaking go with 10. Just make your top jig loop knot go through the loop twice to get a better seated knot. I do this and if I hang up the bottom jig it usually breaks below the loop knot and I will only lose one jig.
You can also make a tandem rig by using a lighter line on each and using a swivel clasp to attach them. Tie a 12" piece of 4 pound mono to a jig and make a small loop knot at the top to attach to the swivel clasp. Make another 4 or 6 pound test 24" leader and tie to another jig and make a small loop knot and top and attach to the same swivel. Now you have two jigs, different depths, different line strengths and if you hang up only one will break from the clasp.
I also take a 24" leader and tie two jigs to each end and then I "fold" the line making the jigs hang at different depths and tie a loop knot at that point in the leader. I now have a tandem rig to attach to the clasp. If one jig hangs it usually breaks below the loop knot and I only lose one.
I sue 8 lb test on my reels and use 6 and 4 lb leader lines. Save more gear this way.