With cat proofing the garden, there are various ways of doing this. One of our kitten families recently cat proofed her garden using Katzecure. She says it is brilliant. There's a link for it here:
Katzecure – cat fencing for cat breeders and cat owners alike
Or you could look at using an overhang system? This can be done by yourself quite cheaply with wire and trellis etc. Have tried to find pics on the internet for you but can't find a darn thing
There's also the option of building a cat run which again can be cost effective if you are handy with DIY
I honestly don't know if leaving them to it would sort anything out. It's possible that your boy may actually become very distressed. I'm hoping someone else on here will have some advice for you.
Just found this online as well, don't know if it's any good though?
cat proof garden - Compare & Save at WinBuyer.co.uk