We do a little of the tagging too. We're all at home, every day - our son studies via distance education and hubby and I share the teaching. I get up super early and check email, do forum rounds, etc, so when I DO get started, I'm not wasting time on that stuff (though winter IS on its way, so no telling how long that will last). Hubby and son do schoolwork in the mornings and when they stop for a break, he heads outside, so I have that time available to do the complex, mentally challenging stuff. After lunch I teach him for an hour or so, then he's off playing so my time is my own again. Maybe I'm lucky in that he usually entertains himself or visits a friend down the road who also homeschools, and most of the interruptions are because he wants me to get something for him, so it's quick enough that I can do it and get back to work without losing my pace. I'll also stop once an hour for a quick break and have a little catch up with them then too.
I think the best you can do, in order to stay at home, is to stick with the tagging, and make sure the kids know to come to you when it's your wife's work time, and to go to her when it's yours. I don't know how old they are, but if you can find something that they love doing and don't need a lot of help, it can occupy them for ages so it's easier on both of you.