Poor Progression

Puggy's not doing so well on the sit when halting homework. I said he caught on what's expected of him very fast during the heeling homework for the 1st week. I've trained him for 2 days & he still can't auto sit when I stop walking. He sits about 50% of the time when I give the command without me pushing him down. I'm so scared that by the end of the week, he still won't be able to auto sit.

Anyway, I tried using the choke chain on Ton Ton at home since the tiles are very smooth & unlikely to cause abrasions. The moment he sees the chain, he went to hide under the chair. Fine, I dragged him out, put it on him & started walking away. He struggled with me & even went into a down position. Still I continued walking like we were taught. What happened next is either going to make you laugh or cry. He got so scared that his shit dropped out onto the floor. Is that a conclusion that he's not suitable for choke chain training?