Google Sheets – How to Create Dynamic Borders for Columns

This is how such a script can work. The variable startRow is fixed at 12 here - an alternative option is to take it from the current selection, which would be startRow = sheet.getActiveRange().getRow();

The script then searches column A for "end of list" text, and then deletes the required number rows.

function deleteRows() { 
  var startRow = 12;
  var sheet = SpreadsheetApp.getActiveSheet();
  var colA = sheet.getRange('A:A').getValues().map(function (row) {
    return row[0];
  });
  var endOfList = colA.indexOf('end of list') + 1;
  if (endOfList > -1) {
    sheet.deleteRows(startRow, endOfList - startRow);
  }
}

Note that this is really deletion, not merely clearing out the rows. To clear the content but leave the rows, replace the line with sheet.deleteRows by

    sheet.getRange(startRow, 1, endOfList - startRow, sheet.getLastColumn()).clear();

I expect you have already solved this, but still wanted to post my solution for others who might have the same issue. I edited user0's answer to allow for dynamic criteria

function onEdit(event){
  var ss = SpreadsheetApp.getActiveSpreadsheet();
  var sh = ss.getSheets()[0]; // 0 == first sheet.
  var cellRange = SpreadsheetApp.getActiveSpreadsheet().getActiveRange();

  if (isWatched(cellRange)) { // Check if edited cell is the one we're watching.
    if (event.value == "TRUE"){ // If the new value is true, protect the data
      setProtected(cellRange)
    } else { // If the new value isn't true we remove the protection (this allows you to remove the protection by unchecking the checkbox)
      var protections = sh.getProtections(SpreadsheetApp.ProtectionType.RANGE);
      for (var i = 0; i < protections.length; i++) {
        if (protections[i].getRange().getColumn() == cellRange.getColumn()) { // We only check if the column of a protection is the same
          protections[i].remove(); // remove protection.
        }
      }
    }
  }
}

function setProtected(cellRange){
  // Sets the desired range to protected
  var ss = SpreadsheetApp.getActiveSpreadsheet();
  var sh = ss.getSheets()[0];
  var protectedRows = sh.getRange(cellRange.getRow() + 1, cellRange.getColumn(), 7); // We protect the 7 rows underneath the checkbox

  protectedRows.protect().setDescription("Protected cell");
}

function isWatched(cellRange) {
  // Check if cell is watched
  if (cellRange.getRow() == 3){
    return true
  } else {
    return false
  }
}