Commercial bobber stops are available but I have found that the cheapest and best are the ones cut from fine 1/16"ID rubber tube.
To make a stop cut a short 1/8" long loop of tube .Run your line through the center hole lead the line outside the rubber band and pass it through again. Pull the line tight and a small rubber stop forms on the line which can be easily slid up and down but will hold a bobber in place. Install one stop above the bobber and one below.
If you select a small diameter rubber tube the stops will pass through the gate of your levelwind and can be cast without disrupting the cast. This allows you to put on a stop for a sliding float for fishing deep pools.
I HAVE FOUND THAT ALL THE knots recommended by powerpro work very well for the uses recommended. The knot joining pro to mono I have found useful is the Albright with a lock . I find it handy to tie on a short 10 'length of mono on which floats are set and swivels sre tied on. I use mono of about 4 pounds lighter rating than the power pro.