Almost every officer carries a knife as both a back up weapon and as a tool for daily use. For most officers this is usually a manual (thumb flip), automatic or assisted opening clip knife that is carried in the strong side front pocket. While this is fine for a tool it has some limitations for a back up weapon.
First, if you are in a fight and cannot access your handgun it is unlikely that you will be able to access a knife in the pocket next to your holster. The exception to this is if your handgun has been dropped or knocked away.
Second, if you are struggling with a subject over control of your weapon, your strong hand is often fighting to protect and maintain control over your weapon. Your weak hand needs to be striking your opponent. You want to be able to use the knife with your weak hand. It is nearly impossible to reach across your body and access a knife in your strong side front pants pocket with your weak hand.
Third, we all know that in stressful situations we lose the ability to perform fine motor skills such as thumbing open a knife, or disengaging the safety on our automatic knife. It is nearly impossible to do those tasks with your weak hand in a high stress situation. The operating controls on you knife will usually be set up for your strong hand and be almost impossible to operate with your weak hand.
For these reasons you should consider carrying another knife. Look for a short fixed blade knife that can be carried on your weak side. There are a number of different types available; push knives, angled blades and straight blades. The one I use can be worn on my pants belt behind my duty belt. Most agencies don’t want their officers walking around with a sheath knife on their duty belt. The handle sits somewhat concealed behind my magazine pouch. Either hand can easily access it and there is no folding blade to manipulate. It comes quickly out and into the fight.
The clip knives are great and have many uses. I still carry my clip knife in my gun side front pocket, but I have my fixed blade knife on my weak side as a back up.