I can empathise with your situation – toilet training can be exasperating, especially when you’re living in a rented house!
Dog toileting problems are usually very logical to the dog but often difficult for us to understand. Dogs are creatures of habit and if their routine is changed they will often exhibit signs of stress or seeming confusion as to what’s right and wrong.
There are a few reasons why Buddy may not be toileting in the courtyard when you’re out. If there is no to little lawn in your new place then he may simply think that the carpet resembles grass more than the hard surface in your backyard (I know my dogs have been guilty of this!). If he is following you around constantly then he may be suffering from separation anxiety when you’re not home and venturing into the courtyard may be too far from where he thinks you may reappear from. This can occur even when you’re home. You’re on the right track removing any scent of previous accidents properly and it’s great that he’s happy to use the dog door as many pooches take a while to adapt to these. To correct the problem and encourage him to toilet outside you need to be persist and present – taking him out often and rewarding the behaviour with a treat and positive tone of voice. You can also associate the act with a command like ‘wee’ or ‘toilet’ by saying this every time he does it outside. Eventually it will click that you want him to toilet outside and he will do it by himself. If all else fails you could invest in a pet loo. He would take to the artificial grass quite well and it would enable him to do his business inside but localise it one purpose built spot. I have used one of these for my two dogs and it worked very well.
Lastly, don’t give up! Buddy want’s to please you and he will be just as happy as you when he’s doing the right thing!