Naf Off Extra Effect Gel, Equine Fly Repelllant. Naturally Effective protection against flys, horse Fly and Insect Menace. by Naf Off. Protect your horse from biting insects and flys this summer with Naf Off Extra Effect Gel. Great product for horses who don't like to be sprayed. Resealable tub. Pink is in, Flies are out.Unfortunately, due to flying restrictions we are unable to deliver liquids, aerosols and gels outside the UK.