Have to relink files every time I open document in Indesign

Hope someone can help me with this. Every time I open an InDesign file it says the links to my imagery are missing, so I go in and relink them and save the file then for a short while it says that I have 0 errors and everything is good. But as soon as I close that InDesign File and reopen the exact same one it says that those same files are no longer linked. I've relink these files like 15 times, I'm not sure what is going on. Even sometimes if I am working within the file and it says 0 errors, within an hour of me working in that file it will say that I need to relink my files. How does that happen while I'm still in it and haven't touched those links.