Sorry for weak English. Imo best option is to decrease their movement speed to 2-3x faster than they now walk. But make them killable only with headshots, body shots might only slow down them a bit or make them fall (lay animation and stand?) also they'll be able to kill you by just 1 hit. They should also attack you from bigger distance if they see/hear you. Gun shots should make them fallow to noice source for 2 mins for example. They also should fallow you for 2 minutes and if you ran away they go back to their spot.
