A good-quality handsaw will remain sharp through hundreds of cuts if you take care of the tool. When the saw is not in use, protect its teeth from dulling bumps and drops by cutting a section of old garden hose as long as the blade. Slit the hose lengthwise, then slip it onto the saw, as illustrated. (You can also protect blade for a bow saw and circular saw this way.)
When working with a handsaw, always check the board before making a cut to make sure you're not going to hit a nail or screw. Never cut a board that's dirty or covered in concrete; the abrasive grit will quickly dull the sharpest saw.