Khani,
To get back to your original question: catching Ghost crabs.
Blades idea of the plastic bucket is brilliant and is almost always successful, providing there are ghost crabs around. To elaborate a little, the hole in the sand needs to be the size and depth of the bucket, then sink the bucket into the hole such that the lip of the bucket is level with the beach / sand. Then drop a few chunks of sardine bait on the sand around the bucket and a few into the sunken bucket. The crabs will be attracted by the smell, and then fall into the bucket in pursuit of the bait in the bucket. Obviously, they can't get out for the same reason Blade stated.
I've used this many times when fishing at night - you usually have a bucket full of ghost crabs in no time at all. Then simply keep what you need and let the rest go.
This way you dont have to chase after the crabs, you can sink your bait bucket, then go make up traces etc, and come back and collect your bait when you're ready to bait up.
Cheers
Gilly