Used for centuries as a permanent seizing for the ends of ropes. Double over the end of a length of whipping twine and hold it with your thumb against the end of the line to be secured. Wrap the twine tightly around and around for a distance equal to at least the diameter of the line.
Pass the end of the twine through the loop and then draw the other end of the twine through the wrappings until it is about half way. You may well need to grip this end with a pair of pliers to exert enough pull. Use strong synthetic twine so that the whipping does not rot on exposure to weather.