What I do after tying a standard bowknot (what I believe all kids in USA learn before school age) is expand the loops so that the two free ends of each lace are an inch long. Long enough to not slip through and undo the loop, but short enough to be clear of any part of the unicycle. Then the loops which are extra long now I pull tight toward the toe of the shoe and tuck under the laces. I pull them back toward me, trapping them under as many of the crossed laces as they’ll get under. It’s pretty quick and easy to do. Admittedly I don’t do much in the way of “extreme” riding, but in nearly three years I’ve never had a loop slip out and do me harm.
Alternatively, I found this in a search.
And also here.