[General] How to disable transport for certain unit types

[Barade]

I don't want certain unit types to be able to be transported. Is the only way to create a custom trigger and to stop the transporter on the loading order or unload them after loading?
I know there is a field of the transport size so maybe I could use a bigger value than available slots?
Isn't there a flag which prevents a unit from being transported?

 

[Razorclaw_X]

Technically there is-- the 'Suicidal' flag by default does not allow units with that set to enter a transport (transports in turn are set to pick up 'Non-suicidal' units). The real trick is how much you care about Goblin Sappers and Tinker bomb drones getting on transports.

 

[Shar Dundred]

Set transport size to 0.