Agreed. Always over. I will actually switch it at other people's houses if it goes under.
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Toilet paper holders are wall decorations at my house... The roll can be found standing up on the back of the toilet, usually with a extra roll or two next to it. Turns out that my dog uses the tp holders like tp dispensers, and will sit and munch tp until the roll is depleted. On the bright side, when this happens, she manages to wipe her own rear, from the inside out.
(Unnecessary comma, but you get the idea)