a millstone round your neck
millstone around (one's) neck
A heavy burden. I wish I hadn't bought that house—the mortgage is a millstone around my neck.
a millstone round your necka very severe impediment or disadvantage.
A millstone was a large circular stone used to grind corn. The phrase alludes to a method of executing people by throwing them into deep water with a heavy stone attached to them, a fate believed to have been suffered by several early Christian martyrs.