I used a shampoo bottle with a click-on cap as a dildo for my ass in a shower. Of course the cap un-clicked and was left in my butt... When I felt something was not right and saw a missing cap, I panicked and clenched my butt, pulling the cap further up my rectum. I squatted down and started pushing out, while fishing for it with my fingers. Somehow I managed to pull it out, not without some blood as it had a rough edge. Fortunately, nothing major, in a few weeks I was back at it again... this time a bit smarter about the toys I used.
no matter how wide and anchor-ish the base is - if it as wide as the plug itself, or big, but flexible, I always tie a lace to a base.
Actually, it's not the base that prevents the plug being pulled inside, but the neck that must be long enough for the bulb to pass both sphincters. If the neck is too short, when plug is inserted, the lower part of the bulb is stretching the inner sphincter, as the sphincter contracts it pulls the bulb further in, with a neck too short also base comes in if it's not really oversized. This is why so many princess plugs get lost in the butt - the smaller ones have short neck and really small base. With a long enough neck, the base can be small and shaped more comfortably, e.g. a sphere is a superb comfy shape, no need for a anchor style base, as the sphincters rest on the long neck and plug is not pulled in. OTOH, a neck too long lets the plug move and the neck passes up and down through the sphincters, causing friction, "eating" lube and in time becomes bothersome. That's why finding the right plug that can be worn for hours is not that easy.
edit: typos...