Notating the middle pedal

[Motrax]

While writing a little composition, I realized I don't know how to notate use of the middle pedal. I've never come across it in the music of others, so I happened to never learn how to do it. Can anyone help?

Thanks in advance!

-M

[quantum]

One of my professors used it in his composition:  notes were first held down silently indicated by x shaped noteheads.  "Sos" with a solid line followed under the staff and a * for release point. 

If you need to hold all the way through a piece, I guess its pretty easy to just put 1 bar before the start of the piece all the notes you need to hold, and just say hold. 

I guess for more complex notation you could go to 3 or 4 staff notation, using an independent staff for the held notes. 

I just checked the Alfred Blatter text, and he recommends diamond shaped noteheads for silent holds, and the "Sos _______________|" for pedal.