We use a baby gate in the middle of our staircase to keep our guys from
going all the way upstairs.  We also have the type where one side slides
behind the other, and both sides have the thick plastic netting.  I went
to Michaels, (or any craft type store), and bought a piece of the thick
poster board.  It's maybe a 1/4" thick, and has foam in the center.  We
cut it to fit each side, and used twisty ties to hold it to the plastic
'netting'.  (We poked holes in the right places to line up with the
plastic).  The board is smooth so they can't get a foothold, and the
twisty ties are neat, and the guys can't do anything to them.  This has
foiled them for about 6 months now.  One of the guys did figure out that
he could squeeeeze though the tiniest space between the one side of the
gate and the step, so we put a 'Where's Waldo' book there, and he can't
get through.
 
At another doorway, my husband cut a piece of plywood about 2 feet high,
and we put a piece of leftover carpet tubing on top..  I LOVE this one.
My daughter and I can step over it easily, but the guys can't get a grip
on the tube..
 
Just thought I would add what has worked for us...
 
Sharon L, daughter Rachel, Nanook (I'm luckey I'm so cute because I get
into so much trouble) and Snowford (you mean those speakers AREN'T for
climbing???)
[Posted in FML issue 3669]