I had a parent who did the long drop off thing despite my best efforts to get them out the door. It was like they didn't want to leave until child was crying so the parent would feel better thinking the child was going to miss them. Ugh parental egos.
I finally wrote a letter stating the reasons for quick drop offs/pick ups and that it benefits the child not to be driven to hysterics before parent leaves. Arming the parents with this knowledge and what is expected from them, I am now forth right and tell them to say good bye in a firm manner.

I would also send a letter to no diaper parent. I always have extra diapers around and would not hesitate to put one on this child after parent leaves. That is ridiculous.