The Hip Hump is a great way to escape the Knee On Belly position. The KOB can be a nightmare and really drain your energy, especially in the later minutes of the round. This escape is great because it focuses on strong fundamentals and encourages a large range of hip movement.
The fist step is to lay your arm around the back of the thigh. This is in contrast to the defense that a lot of people have learned where you push on the knee. Often times when I go to KOB I'm not looking for any particular submission but I AM hoping that they push on my knee so that I can take control of that arm. Be careful when escaping the KOB position and if at all possible avoid pushing on that knee.
Once you lay your hand by the thigh and your other hand takes control over the outside leg it is time to start moving your hips. This is not a resting position and if you give your opponent an opportunity to transition you're going to find that you are in deep trouble.
I like to make space by shrimping my hips out and guiding the knee (with my bicep) into the space in front of my hips. Once that knee hits the ground it is time to start pumping with your hips. The goal is to knock your opponents knees out and have their butt land on your stomach/hip area. Once this happens you are in business.
Once your opponents weight is on your stop hip pumping and turn the corner for a 180 degree shrimp. There will come a point where it will feel like you can power them over by bridging, please RESIST this urge and finish shrimping. If you bridge your opponent over they will land to close to you and you my run into a scramble. If you continue moving your hips out in the shrimping motion then you will come up at a 90 degree angle and it will be very difficult to resist.
Give this a try and see if you like it. I am a huge fan of anything that involves increased hip movement! If you are having problems with this move it is probably because you are not hip humping hard enough, with enough force and your opponents weight is never transferring to your body.
In the event your opponent out runs you and you hip pump 10 or 15 times without being able to take their knees out from under them then going out the back is the best option (especially because you have the underhook and your opponent is moving in the opposite direction of a back take).