If you want to move money around in large quantities, either to buy a house/ship/equipment, or to play the slots game, then make sure you have it all banked first and then attack someone with a higher level than you in order to place yourself in the injury ward.
Once you are in the injury ward, no one will be able to attack or mug you in order to take any money from you. It allows you to basically do anything with any amount of money you want.