For some reason my hide/show lines icon went missing yesterday.

I have two questions.

1. How do I get this option back?

2. How can I hide lines that overlap each other? If I have two parts butting each other, I have to hide one component, hide the line, then hide the other component, bring the other component back, then hide the other line.  It's very time consuming and annoying....becuase half the time it doesn't work.

Thanks in advance.