I need to select a random subset of spatially independent grid cells for a species occupancy modelling study. I defined my sampling units as 100x100m grid cells covering the entire study area. However, these grids are continuous and not independent from one another (see attached). I would like to select a random subset of grids (let's say 50%) which is at least 100m from the closest grid (between each grid cell there must be at least a 100m distance). Any advice on this will be much appreciated, also, I'm using ArcGis 10.6.