Certainly the ground-based midcourse ballistic missile defence system that the Americans have developed is a developmental program, and a number of fairly high-profile failures have occurred.
One fundamental premise, though, is that there will never be enough interceptors to defend against a prominent actor, Russia or China, in the ballistic missile environment. You are only dealing with onesies and twosies from a North Korea.
When I was deputy commander of NORAD, admittedly this was 13 years ago, I participated directly in a number of ballistic missile defence exercises in Colorado Springs, because it was assumed at that time by the Americans that we would participate, so they included Canadians in everything.
I was the acting commander in chief for a number of those exercises. I made the decisions about what targets would be engaged and how many missiles would be launched. I briefed the exercise president on what was happening. I got information from a Canadian missile warning officer to tell me about missile warning. I liaised with the American ballistic missile defence system stakeholders, and we addressed the challenges of the exercise through that.
The reality is that we will never be guaranteed that Canadian territory will be defended by the eventual system unless we are part of the equation.