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cat door glass or wood installation

i have a cat door i need installed to glass or a thin ply bottom door window. im unsure what one to use still. i dont think it can be put in current glass in the door so i need it removed and normal glass put in or just a thin ply of some sprt added for now. i kind of need to keep the current glass in one bit to replace when i leave. i do have a concern that the door will be to high from the ground and cats can not climb through it so interested in ideas.