We went through the same thing though and our girl is 5 months old.
First of all.. be grateful he went on the concrete outside... at least it was outside! He is still a puppy and is still learning I'm sure if he is barely 4 months. What really helped us is going back to the basics and taking her out after every feeding, play time, nap, etc. and especially after feeding keeping her on the leash until she goes #2!. We realized we had become relaxed about it thinking she was 'grown up' but it was too soon.
After goin back to basics, we introduced 'Poochie Bells' to hang on our doorknob so that she can run over and ring the bells when she has to go outside. That has helped Tremendously!! While she's still not perfect... she will ring it to let us know when she has to go outside and we will take her on her leash to her 'potty area'. Sometimes she rings it and then goes right there on the floor... but hey she really tried and it might of snuck up on her... I'm sure she's still learning how to hold and control it and it might catch her off guard sometimes! But the poochie bells do open up communication as a way to let us know. We just took a trip across country and she would ring the poochie bells at the hotel too (still had accidents at night because our routines weren't the same). So after she has caught on to the poochie bells and you go to your dads, you can hang them on the door you will take your pup out of and make him ring the bells and take him outside immediately so he knows where they are!
It might be something for you to try... just keep at it, it takes a lot of work just like having a kid... he's still a young baby puppy and I'm sure he will catch on soon!