Hi Ohiomonarchmama! I like your name. I hadn't seen any of your postings before I chose a name, and didn't mean to be a "mimic" , but you know what they say: Great minds think alike.
What I have tried to do with my milkweed is to locate it at the back of my perenial beds and at the back edges of my lawn. I have taken the large coffee cans and removed the bottoms then sunk them level in the ground and that has worked well for both mint and monarda so I don's see why it wouldn't work for younger milkweed. The older a plant gets the deeper the root goes and the more underground system it builds and sends out runners, but any that have escaped my barriers were young enough and close enough to the surface that I would just transplant them.
The plastic edging that John mentioned sounds like a great idea though. I am going to give that a try in one of my gardens where I would like a big patch of it but want to keep it contained. It was more difficult when I lived in town as the neighbors just see them as weeds and can't understand why you would want to grow it. My landlady that I rent my mobile home lot from was not happy that I was growing "weeds" and wants them all moved before I sell my place. Now that I have a place out in the country it will be much easier to get a nice established plot of it going and won't have to worry about how much it spreads.
Great way to help your friends appreciate milkweed is to invite them to watch the transformation from egg to butterfly, and eight times out of ten they will be "hooked" and asking for plants of their own.
This summer I have shown the young neighbor boy how to identify milkweed and find eggs and giving him advice on raising them for his Boy Scout project. It feels good cause even though I am moving away I will be leaving someone behind in the neighborhood to carry on.