I was thinking of using temporary hit points to measure the damage my creature takes before it takes damage. Now to make it fair and reasonable I plan to only use a certain number of hit points in the creatures stat block. So essentially when it's about half damaged per the stat block, they start to draw blood on the creature. It's only for a specific encounter this is not a rule I plan to live and die by at all. But would temporary hit points be the proper way to measure it or should I just have a damage counter instead. IDK maybe I'm thinking too hard on it.

Loss of HP doesn't mean wounds and loss of blood. Hit Points are an oversimplified general concept of vitality and wellness. The loss of hit points can just represent the wear on the body as you evade, etc. It also represents the will to survive. The experiences of battles, traps and whatnot can wear on the mind, not just the body. 

You can totally have it that the creature doesn't show any signs of injury until half their hit points have gone - there's no need for a special feature or whatever. You just describe it. In fact it is very common that a creature is not "bloodied" until they're down to half-health and only when "bloodied" do they show signs of damage or fatigue.