Yes, I still have one of BD’s old collars in a jar in the garage - and I have found plenty more over the years in different spots - he hated them and was quite adept at getting rid!
I’m also in two minds now about keeping cutting back - BD chose his own time and place to go and die and we never found where. I’ve always wondered if it was under the shed, where he first lived for some months when he first adopted my garden but before he came in to the house and adopted me but he also loved this bush and would hide there for hours waiting to pounce-out on prey from it, so he could be there. However, I’ve probably cut it back enough - ts good for all the wildlife in the garden but it had got right out of control and was beginning die back in the middle, so I’ve removed about half of it, right back to healthy growth that will come back.
I think if he went back to the soil in either of those places that would be a good way to end up for him and leaving him undisturbed there sounds good, you don't want to be coming across that (it could be that there is nothing left there for you to find, but it is not something you want to test as it could be really upsetting).
One of my difficulties was not having anywhere to bury Radar and having to get him cremated, which I don't favour and I think made it more upsetting. I've buried previous pets in my parents' garden but they are council tenants and getting on for 80 now, plus I have a difficult relationship with them anyway, so I opted to have Radar cremated and I found it really difficult as it is not something I would ever choose if I had any other more private burial option and it feels like a halfway house towards getting him properly buried somewhere close to me, an option I don't have right now. I find it difficult to look at his casket because he should be in the ground.
I do think the proper cycle of things is to go back into the earth and provide new growth - however new age and wanky that sounds (and I grew up in the country, I know full well to put paving slabs down on top of a pet's burial for 6-12 months to prevent scavenging, THEN remove them and plant a memorial)
If I ever get a place with a garden one of the first things I am going to do is dig a grave for Radar's ashes (they are in a cannister inside his casket so I can undo a few screws in the base in order to remove and bury the ashes) and plant something on top for him. (I hope I might start to feel some peace then). Or if I die before then I want any deceased pets ashes buried with me.
(Also heads-up, if I have a garden that I own outright when I die I want to be buried there myself - it is completely legal as long as the burial is on private land and the burial location is logged with the registrar, you don't need planning permission, and fuck property prices, just hire a JCB and stick me right in there, bury all of my pets' ashes with me, that is what I want).