Here are some pics. As you can see I used the wrong tool to make the hole bigger 
. I attach them to the wall with Quake hold putty from Amazon.
This is the one I use on the stairs. It’s under the hand rail so its somewhat hidden and about 3 feet off the stair tread. Neither the dog (small dog) or cat set it off. The other one I use for the bathroom door is angled using the Quake putty (putty built up on one side) and I put some tape on the tube to really limit it’s field of view.
You can use just about any sensor you like, providing you cover the bottom part of the lens with white (so it’s not visible) tape. That way it will not see the floor anymore. Playing with the width of the tape you can adjust for pet’s size.
It’s also a good ideea to have a sensor with adjustable sensitivity for even more control.
I use a MultiSensor 6 for outdoors, protected from weather and USB powered… Never had a false and it worked perfectly down to 21 deg. Handler https://github.com/erocm123/SmartThingsPublic/blob/master/devicetypes/erocm123/aeon-multisensor-6-advanced.src/aeon-multisensor-6-advanced.groovy
I also have 6 Zooz ZSE09 for inside. No false either after adjusted sensitivity. Handler https://github.com/erocm123/SmartThingsPublic/blob/master/devicetypes/erocm123/zooz-mini-sensor.src/zooz-mini-sensor.groovy
