This can be a surprisingly difficult problem, more so as numbers of outputs increase.
The problem with PTCs is that the output MOSFET has to withstand the output current while the PTC heats up. If your supply has a high current capability, this can easily be tens of amps.
The simple answer that is to use a bug chunky MOSFET - in practicce you need at least a TO-252 style package, however this costs money and PCB space, and the increased gate capacitance may cause problems in PWM applications.
I recently did a 48 channel 24V LED dimmer with 1 amp per channel output,so you potentially have a 50 amp PSU waiting to vapourise the FETs in a fault condition.
For space reasons I wanted to use SO-8 dual mosfets, and I found that protecting these with PTCs wasn't possible - the FET always blows first.
The answer I found was these
nice internally-protected FETs for automotive applications
. OnSemi also do some similar devices - I don't recall the part mumbers.
These switch off in a few microseconds when shorted, making them indestructible.
The only downsides are that the internal current-sensing resistor makes them dissipate more power than a standard FET, and being aimed at the automotive market the leadtime can be quite long.
You could make a similar arrangement with standard FETs and a current sensing circuits, and you could use comparators to keep the drop on the sense resistor down.