I have great sympathies for many railroaders in the United States. Over time I have read about squirrels, deer, snakes, scorpions and all manner of unwanted visitors. Luckily it is rare for railroaders in the UK to suffer from these varmints.
However, one problem I have had for around four years now, after getting another dog, is his desire to remove small figures and animals, plus the odd barrel or two and small lineside features from the ROW or station areas. Consequently I had to remove all of these items which was a nuisance as they added to the ambience and interest. I have had many dogs long before the railroad was built but knowing dogs propensity for chasing cats, birds or anything that they feel is an intruder, has meant no signals or other lineside features as they would not survive very long out there.
The occasional burying of small items of food, when an animal in not hungry, has been an inconvenience, but not on the scale of what Ron (the OP) has experienced. One thing for sure is that outdoor railroads do require a fair amount of maintenance.