hell or high water, come
Also, in spite of hell or high water . No matter what difficulty or obstacle, as in I'm going to finish this week, come hell or high water. This colloquial expression, alluding to the destructive forces of hellfire or flood, was first recorded in 1915 but is thought to be older.
The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.