I was disappointed by all of the gutter guards available at the Big Box stores, so I got some 12" flashing and made my own.
The wind clears most of the heavy leaf litter off when its dry and heavy rain washes it over the top of the slot between the guard and the gutter. Any water short of a deluge pretty well follows the rounded contour of the fold and drips into the gutter.
Slipped under the edge of the metal roofing or shingles and retained by the metal building screws or shingle nails, the guards stay put even in considerable wind, they are bent to hover just above the hanger nails, following the slope of the gutter and are flexible enough to allow entry of a hose for a cleanout.
Some material is going to accumulate in the gutter no matter what .... silt, if nothing else ....
The sketch should explain it all...
Terry