As your athletes get mentally tougher, try changing up the tempo of the reps instead of increasing the resistance.  Try a few sets of a protocol called “super slow”.  In this protocol, the concentric phase is executed in six seconds or longer with perfect posture and form.  After the concentric phase, follow it up with a six second, or again longer, eccentric phase.  When executing a pulling exercise, add a six second or longer isometric between the positive and negative phase of the lift.