Personally I think you could justify and be allowed to have an air gun range in your garage. I know a guy that used to shoot 10m air pistol and had his own indoor range. I dont know if it was signed off on by the LRD or not. it was quite some time ago. Not sure you would be able to shoot pistol at home these days but Rifle perhaps as long as there was no way pellets could leave the building and not ricochet back to the shooter. which sometimes happens at professional pistol ranges.
If It was just mine dont know which way I would go notify the authorities or keeps it all completely hush, hush.
As far a rural property goes. I think constructing a significant backstop and other earth works to protect your neighbors both physically and from noise is acceptable. In these cases I think it is always best to involve and explain things to your neighbors get them on side. Sow a seed that you could do this and that to minimize impact to them. If they go for it and take it on as their idea or a favor you are doing for them. Then you are not going to get any complaints at least you would be told first if they had any concerns. Dont go inviting friends to shoot every weekend all day sort of thing stuff that is outside what is in the regs.