Another getting rid of neck grab technique. Here you need to be strong enough to lift the one behind you.
But my personal favorite is to fold your knee and kick behind targeting the bone between his knee and feet. If that works you are free. If not he will for sure move to protect his leg, loosing his grab hold and you can set lose with a little effort.
The intuitive but wrong way is to pull his arms to open the lock, which wont work.