There may come the day when a suspect is attempting to take away your duty weapon. You will be busy fighting for weapon retention and may not be able to get to your backup. Your knife maybe the only weapon you can access. That is if you can get to it. Where do you carry your knife? If its on your strongside, like the majority of officers, that side will be a little pre-occupied with weapon retention.
I recommend that you carry your defensive knife on your support side and you should be able to deploy it one-handed. Watch this video for a couple of tips.