If this problem exists use one of the environmental controls mentioned above. Flush with a clean liquid. Check with your seal manufacture for the minimum amount of flush that is needed. At shaft speeds below 2900 rpm. filling the seal cavity with a compatible grease is usually satisfactory. Increase the seal clearance in the stuffing box area.
Replacement back covers with extra large stuffing box designs are available for most pumps.
Bolt on, large diameter stuffing boxes are also available in the after market. In some cases two hard faces also helps. Recirculate to the suction side of the pump when possible. This will circulate cleaner fluid from behind the impeller, through the stuffing box, and then back to the suction side of the pump. Original equipment manufacturers do just the opposite by having the stuffing box fitting connected to the discharge side of the pump.