I've got a Timex Expedition that I've had since high school. That means I bought it some time during the early Triassic. Its stainless steel backplate is held on with four Phillips screws and I have never in many decades had any problems undoing them when I need to replace the battery every six years or so. It remains resolutely waterproof. I know this because it lives outside rather frequently: at the moment I have it stuck to the gauge cluster on one of my motorcycles with Velcro.