I invite them over for dinner, LDS missionaries are notoriously hungry. That way they set aside a whole evening for you and they are too polite to leave.
I never let them pray, rather I respond with ‘good idea’ and either my husband or I pray instead. We discuss and debate and at the end of the evening, when they get to giving their “LDS testimony” I respond with my testimony countering each of their points.
After the last time I did this, they crossed on the other side of the street rather than walk past our house for almost 3 years.
He all have our methods.
Reaganaut, I have no doubt that you and your husband are both wise and kind. May you continue to so treat Mormon missionaries ... if you have the chance.