There is so very much to say on this topic. Some of the stories I have are both comical and sad. I'm sure you have your share as well. In my experience coaching/managing a youth travel baseball team with a high school coach we can sum it up into two problem areas that need to be taken care of up front to avoid the helicopter parent:
1) evaluating talent - most parents get it, other parents not so much. As a coach, if you can educate parents on their sons strengths, weaknesses, and development areas (document it) you are there. Also, I think as a coach, you need to reinforce the fact that it is a monarchy not a democracry. If they go to the AD, you have a document and stats, and it is going to be a short conversation between you and the AD.
2) Expectations and communication - constantly communicate expectatons with the player and the helicopter parent and make it the same message. In a lot of cases the non-helicopter parent will understand what you are doing.
These two areas worked for us, and I'm sure there are many other suggestions. The challenge with HS baseball versus travel is the number of parents, and their experience level. BTW...The most successful HS coaches in our area are the "old school" ones that take no ****. In most cases, the helicopter parent is not inclined to challenge them because there is NO open door policy even when they say there is one.