If you want to use linepicks then a simple method is this:
while walk is selected, and the player begins to move in a direction (ie presses cursor key in some games) then perform a linepick at the location where the character is about to move to, straight down for a reasonable distance. If it returns '0' then no mesh has been picked meaning the player is moving towards a sheer drop. If that is the case then disallow the move.
while walk is selected, and the player begins to move in a direction (ie presses cursor key in some games) then perform a linepick at the location where the character is about to move to, straight down for a reasonable distance. If it returns '0' then no mesh has been picked meaning the player is moving towards a sheer drop. If that is the case then disallow the move.