In a honesty, personally, I found it too full on and wondered if the dog was over stimulated.
There's alot of training for a 4 month old. Like the 4pm-6pm the dog is consistently being stimulated and may find it too much.
Infact, 4pm to after his last walk is all quite stimulating. Which can be good, but too much can make a dog over tired. Which means excitable, naughty, bite etc.
And if its not working for you and feeling like hard work, you will end up with cocker than needs pts of stimulation and may find it hard to settle. It needs to be enjoyable for you all.
But on the other hands if the games are too easy, they aren't doing their job either.
I would personally recommend you work on more, out of the pen chill time if you can. Maybe do shorter training sessions and leave a gap between training and snuffle mats and enrichment. Recall training can go on all day, in bits calling the dog to you on occasion for no reason than to give a treat.
Also the digging the garden up etc, they do need to be watched every minute. Our youngest was terrible. We got her just before lockdown. Last summer we had to keep the door to garden shut with windows open so she was only out when we were and we could watch her every second and tell her no as she started. This summer she has been great. But it appears he does that if he isn't engaged by you. Which again, could be a sign he is learning he always has to stimulated and isn't sure how to settle himself without being in a pen.
Does he get off lead walks? Total recall is an excellent book for recall and keeping a dogs attention on you on walks, which is the key to recall.
Cockers can be difficult because the line between bored and over stimulated can be very fine.
Have you every thought about gun dog training? Great for working cockers and their owners even if the dog will never actually be a gun dog.
He will probably always follow you every time you get up though. That's fairly standard.
Working cockers are fabulous dogs but do need a strict, but loving hand and getting the balance can be tricky.