Theri's can walk easily over 1 high walls. Build all walls 4 high or use dinosaur gates as walls and you are fine and safe from most threats.

Best way to trap them: drop trap. Build stone foundations in a 5 by 5 square at least, then build double door frames 4 high (tall), then put a ramp on one side. Peck it with a flying mount, then fly over the ramp and let it fall into the trap. Use a spyglass to tell you the level, then tranq it out. BRING EXTRA tranqs and narcotic. These things eat narcs like candy.