More in Outdoors
Build a gate frame one-half inch smaller than the space you want to fill. Install a "Z" brace from the bottom of the hinge side running up to the latch side to provide extra support.
Make arrow cuts on each end of the lumber and fit it neatly into the corners of the frame. Or, you can cut a 45-degree angle on both ends of the lumber and fit the brace that way as well. Secure the brace with wood glue and wood screws.