ULPT Request: How to convince elderly parents to indefinitely share their location via Find My iPhone?

Have already snuck on their phones and were able to turned on the setting but within hours or days they disappear. So they must get some kind of notification that they then switch off. The husband doesn’t want to wife knowing where he is all the time, that’s why we can’t ask straightforward for him to share with us because then she will always ask us where he is. And if we explain we are putting the setting on as a safety precaution they might also in exchange ask for us to share our location with them, which we are not open to. Any ideas?