The clinch knot is one of the most famous knots in the world to tie securely swivels, carabineers or other things. We use it to fix swivels to fishing lines but it can be used for a lot of other purposes.
The advantage of the clinch knot is, that it will not open it will even get more tied with stronger force. Knots are always the weakest point in your system (in your line). The clinch knot provides about 85% of the strength / load of the line.
Put the line to the eye of the swivel and wind it at least 6 turns around the line while going back the line. When you finished the 6 turns, put the end of the line thru the fist loop of the 6 turns at the beginning (at the swivel) and then to the loop of the last turn. Now pull the end of the line to make the knot tight.
To make it easier to put the line thru the first loop, you can put your finger into the first loop before you wind the 6 turns around the line. Then remove your finger and move the end of the line to the big loop. If the end of the line is too long after you are finished just cut it off.
The finished knot should look like this:
