5 yr old male YorkiPoo peeing in house

Question
I have a 5 year old male YorkiPoo who will not stop peeing in the house, typically on upright objects but throughout the house.  He also has a bad habit of pooping in the garage.  There are no medical issues.  This is not a recent problem we've been going through this off and on for 2 1/2 years or so.  He does fine for a few weeks, maybe even a few months and then it starts again.  He has access to outdoors via dog doors.  I have not been able to catch him in the act, there appears to be no consistentcy in the time of day he urinates in the house.  It does seem however, that is happens mostly when we are home, so it's not a separation issue.  There has been been no changes in the environment, he knows he's done the wrong thing, I know negative behavior on my part (scolding) doesn't work but he is driving me crazy!!  Any advice you can provide would be greatly appreciated.

Answer
First is he's not neutered getting him done will greatly reduce marking

But if that's been done already,the best thing to do would be to crate him,and what you do with that is keep the dog in there all the time except to take him outside,to feed him,to walk him,playtime ect and do that for about three weeks then slowly let him out more,and if he makes another accident,back in the crate he goes for another week

It works because dogs generally like to keep sleeping spaces clean