labrador breaks out of pen

Question
we have a 4 month old yellow lab...she is in puppy training right now and does well on come, sit, etc...our problem is that she has started to break out of her pen by lifting the latch with her mouth, or pushing her head through the fence..i am afraid she might get stuck in the fence and choke herself!..what can we do to stop this behavior?  we let her out every morning and every evening.

Answer
I am not sure what sort of a pen you have.  Is it one of the small chain link ones sold as dog kennels?  If it has one of the conventional fork latches, usually they have a hole meant for a lock.  You could put a farm implement style pin in the hole.  

Usually the fabric is too well secured for the dog to force their head into the gap.  If not, perhaps you could pick up more clips at a home center and fasten it better.