Watch this video from This Old House to learn how to choose a leaf proof gutter.
1 Slide putty knife under roof shingles that are stuck down.
2 Insert gutter protector underneath the shingles, making sure it covers the front edge of gutter.
3 Fasten gutter protector to the roof and or gutter, as specified by the manufacturer.
4 If nails or screws are used, cover each with a dab of roofing cement.
5 Seal down the shingles with roofing cement.
6 Toss dry leaves onto roof and spray with hose to simulate rain; check to make sure the leaves wash off the roof and don't fall into the gutter.