From the Side Mount there is a great submission made famous on the Ultimate Fighter II reality show by Jason Von Flue.
Jason learned the technique at Pedro Sauer's school from inside the guard as a guillotine defense with the gi. He then took the technique and modified it for no-gi.
During one of his fights on TUF Jason pulled the technique off from SM and people have been calling it the Von Flue ever since.
This is a nice choke that will put your opponent to sleep.
It seems like your opponent should be able to free the arm that is over your neck but they can't. Once you have your hands locked you drive your shoulder into their neck to cut off the blood.
Starting from the Half Guard my opponent has the Lockdown. The first thing we need to do is defend the Lockdown. You are in danger of a knee injury if your opponent has a strong Lockdown.
Your left arm should be under his neck to help set up the choke and for base. Your right hand goes to his left knee and then ...
You drive his knee as far open as possible. If they have a strong Lockdown you may need to step your right foot over their right foot so that you can ...
Free your leg and get to Side Control.
Once your are at Side Control you lock up your hands with a Gable Grip trapping their left arm ...
And then you drive your shoulder into their neck by getting up to your feet so that you can use your weight and squeezing the Gable Grip. Be careful not the let your right leg get trapped in Half Guard again.
Here is a video done by James Clingerman where he does a great job of breaking the choke down and showing how it can be used from other positions like Butterfly Guard and from inside your opponent's guard.
