Would it be possible to popup a reminder to close a flightplan? Could be triggered when plane is on ground and standing still or when closing Navigation. Normaly I fly without flightplan but when crossing borders I file a flightplan. If I land on an uncontrolled airfield I could forget to close the flightplan(just did). They send the police to check if the plane had landed an next day I got a lot of angry people in my face.

Just to add to the possible confusion - there is no requirement (or process) to close FPLs when landing in UK.
So, when I fly to France (and probably other European countries), I have to remember to close them myself where no ATC service is provided (like Abbeville).
I don't fly across international borders very often but FPL closure is something I have to positively remind myself about.
I don't think SD is the right platform to provide these reminders. Perhaps your aircraft's post-flight checklist?
Tony Nowak