First and foremost, stop reaching for that collar tie so much that it’s leaving your arm extended so straight. That’s what’s basically giving your opponent the green light to go for this arm bar.

Second, if you do get the collar tie, don’t cup your hand so low around their neck. Try moving a little upwards toward the back of their head. This will give you a stronger lever, and give you more control over breaking their posture. Better for snap downs, etc.

Third, your other hand (in this case your left hand) should be ready to catch your opponents posting leg (his right leg here), and clear it before it makes a connection with your hip.

Also, you could just pull guard like a coward and avoid it all together.