How about trying to just wear something like wellies in the garden for a while, or if your garden isn't particularly stoney and the weather is warm enough, try going barefoot?
My best guess for his motive is that when you put your shoes on he thinks that you are going out, and are going to leave him alone in the house, or garden, which of course he doesn't want you to do. So he does the (very logical) thing that he knows thinks will stop you leaving him, he tries to take your shoes off you - Bless Him! As you have now, lots of times, just gone as far as the garden and then come back in again, whilst wearing your shoes, he thinks that it is safe enough to let you into the garden in them - but once you are in the garden, he knows you might go out without him, and he can't possibly countenance that thought, so he has to get your shoes off you to stop you!
If I am reading your Dear Dogs mind correctly then you need to find ways of stopping, or at least lessening, his separation anxiety, which is often not easily done, but very possible if you persevere.
The only sure fire way of immediately stopping your lovely dog from being destructive whilst you are out is leaving him locked in a crate - but I hate crates with a passion, I think they are both cruel and a very lazy/neglectful way to try to "train" a dog. I don't believe that putting them in a crate ever "teaches" them anything, except to hate the crate! Crates will not stop a dog from being miserable, or from constantly barking or howling while it is alone, but it could actually affect him mentally in such a way that he could become even more anxious, scared and sad.
If you would like examples of how to teach your dog to be less anxious about being left at home alone, there are a great many suggestions on the Internet (but again, PLEASE ignore the ones suggesting or praising crate training). Also, there are of course lots of knowledgeable dog owners on Mumsnet (which is presumably why you are posting here), but unfortunately a lot of them also think that crate "training" is some magic and wonderful new invention that will very quickly give you a well behaved and happy dog - it won't. Your dog's vet should also be able to offer good advice, and maybe some medical help to start off with.
No dog should be left alone for more than a maximum of 4 hours, and if they are going to just be walked by a dog walker in the middle of a working day, that needs to consist of a substantial walk (taking into account the dog's breed, I don't know much about ridgebacks so can't offer you any good advice on that) tailored to it's needs. But he would also need some one to one playing with, and petting, so I don't like, or agree with, the habit of some dog walkers taking more than two dogs from different households, for a walk at the same time. I think it is much better if they just take one at a time - not only does the dog then get undivided attention, but it is also much easier for the D.W. to pick up any dog poo's, and to control any potentially worrying situations.
Of course, your gorgeous Dear Dog might just be behaving like any other puppy I have ever known, who just love shoes and shoe laces, which leads me back to my original suggestion - to not wear shoes in the garden!
Good luck OP 👢🩴🦶