Is there any way I can keep my cats and dog from constantly going to the toilet in a section of my garden ?
To keep cats and dogs from going to the toilet in a certain area of the garden I would recommend a repellent or deterrent product that can be used outdoors, something like Aristopet Home & Garden Repellent for Dogs & Cats.
This can be used both indoor on furniture, potted plants etc and Outdoors, around letter boxes, fences, gates, bins, etc. After a short time, the animals will associate the treated area with something unpleasant and will avoid that area.