Dog still messing in house

Please can anyone give me some mature and sensible advice.

We have a 4 year old yorkshire terrier x pom. He has been castrated and living with my partners grand parents for the last 2 years. He goes out for one walk every day with them but it isnt very far and he doesnt get tonrun off the kead. He has easy access to the garden at all time but has just started messing in the house. He doesnt care where he goes or what he does he just does it. He has started chewing anything that he can and this is outting alot of stress on out grand parents. He is due to come home back us after christmas but i want to be fully prepared for when he returns. I no this behaviour will not stop iver night and i am open to any jdeas that any one may have to help me.

Thank you

one walk in a day is definitely not enough.

unlimited access to garden does not replace the walk. It works more alike toilet break for human.

need to stimulate his brain by play with him, train him. Throw a ball at him to play itself is not good enough. Need to burn out his energy.

You can try with bitter apple spray to prevent the boredom chews but you cannot solely rely on it. Exercising still No.1. Just keep him busy.

Part of the problem (if it has just started) is likely the weather. I would strongly suggest (once you rule out a potential medical issue like a bladder infection etc) that you go back to puppy basics. Take him out every couple of hours and stay out with him until he goes. Praise him like crazy and reward him for going outside. Don't give him the opportunity to make a mistake in the house. If you need to tether him to you then do so. But set him up for success.