My wife and I have three cats - for now. We don't need any more, but it may be a long time before we have fewer.
I've found, to my deep disappointment that cats and model railroading don't mix. My cats would love to get into the trees and chew on them, and then throw them up somewhere else down the line. It sounds gross and it is. The solution (and yes, I did consider amping up the power in the rails) was proposed by a window contractor friend who offered to make an acrylic tent over the layout. The vertical pieces are screwed into the fascia board, and a foot up from the back of the layout I ran a molding strip of wood and then put another acrylic piece sloping down to the sit on top of the vertical "wall" along the front of the layout. The idea was that the slope of the top would allow the cats to simply slip off (they don't). Instead they gingerly walk along the top as if suspended in mid-air until I yell at them to jump down (they do).
The top pieces are lined along the back with Velcro, which is strong enough to hold them in place and yet allow me to remove them when I want to operate trains or work on the layout. Not only does this system keep the cats at bay, it's a wonderful device for keeping the dust to a minimum on the layout.
I wouldn't go to the trouble if I didn't have to, but it seems to be working out.