Car seat harness , child age 7

Son is in a five point restraint forward facing car seat which he is always getting out of and coming to sit in front or stands in back.
If both of us are in car and we can pull over we pull over and buckle him back but it’s not solving the problem

Please suggest some type of harness or restraint I can use to keep him in car seat

Car seat harness , child age 7

I know it is not a car seat harness but what about something like this. It could be clipped onto the car seat straps maybe. They have a model that is a chair strap so it may be worth checking out.

http://www.childharness.ca/

Car seat harness , child age 7

I actually have the child harness for my son from there.
I didn't see the chair strap , but I will look into it
I have just bought the buckle guard from Amazon, waiting to get it and see if it works.. Maybe..
Thanks for the suggestion