Can the garron rule be used to get my husband back into teaching and reduce my support payments?

I am not familiar with a "Garron rule". I presume you mean a Gavron warning, which states that each party is to become self supporting within a reasonable period of time and failure to do so can be taken into consideration in a motion to modify or terminate support. Gavron warnings generally apply to permanent support orders. If you want the court to consider your ex's ability to earn, then perhaps you should be requesting a vocational examination. They aren't cheap, but it may be worth it. No one can be forced to work, however they can be imputed with income based upon their ability to work.