This is a design inspired by Pentland_Designs' "Shoelace Locks". While I like the concept I found their original design to be overly complex and very dependent on tight printer tolerances. This is my take on it.
Use ShoeKlips to easily and quickly secure shoelaces without needing to tie or untie knots. The ShoeKlips clip together easily with one hand and also release easily with one hand. When released the clip will not undo itself all the way but rather stop on a second internal catch. This second catch is sloped so if you do need to completely undo the ShoeKlips you can by wiggling the two sections apart.
Print both parts at once using the file ShoeKlips.stl. If you want to print the parts individually those files are also available. Remember that you'll probably need a pair of these ;)
Lacing it up
Once printed add the ShoeKlips to your shoes like shown here.
You'll notice the arm part is thicker on one side near the lace holes. The ShoeKlips will work either way but they look cleaner if you put them on with the thick side facing out.
On step 4 lace feed the lace back into the middle hole which will give a clean look and cause the lace to clutch on itself. You can feed the leftover lace between the tongue of the shoe and the rest of the laces. You can also add a knot to prevent the lace from loosening but I haven't found that to be necessary.