I'm a pretty lucky guy I guess. My wife never tries to get in the way of my dirt fishing. She knows its my down time and how much I need that. She actually encourages me to go. I've also NEVER asked her permission to buy a detector. She perfers only one of us wear the pants in the house, and that would be me.
On the flip side, he well being is and always will be my number one priority. She knows that. Also, you have GOT to set aside quality time just for the two of you. Every Friday night is our date night. That is pretty well set in stone.
If you can get her into the hobby, thats great. If she's not into detecting, try to make sure she has a hobby of her own she loves, so while you're off detecting she can do her thing.