How can I tell the number of people on my land in a script?

// snippet: (not complete code)

integer gLastCount = 0;

sensor( integer num )
{
    integer count = 0;
    integer a;
    for ( a=0; a<num; ++a )  // check each person the sensor finds
    {
        // if the owner of the land they are over is the same as the
        // owner of the land this script is on, add 1 to the count
        if ( llGetLandOwnerAt( llDetectedPos( a ) ) == llGetLandOwnerAt( llGetPos() ) )
            ++count;
    }

    if ( count != gLastCount )    // if the count has changed
    {
        llSay( 0, "There are now "+(string)count+" people on this plot." );
        llSetText( "Avatars: "+(string)count, <1,1,1>, 1 );
        gLastCount = count;
    }
}