It is important to be 'hands on' in your business, or to employ a competent and honest manager to control the day-to-day running of the business. The more closely you monitor your business, the more likely you are to detect theft or fraud before it becomes a serious problem. This is one strong argument for efficient systems. Note that it's not necessary for you to do the bookkeeping yourself, but it is important that you understand the basic principles behind small business bookkeeping so that you can monitor and control what others do for you.
Many thefts are committed by people who have direct access to cash, stock and/or the company's records. It is therefore a good idea to segregate as many responsibilities as possible among employees and establish good systems where your authorisation is required for some transactions, such as all purchases above a certain value or unusual purchases.
Hold snap in-house audits of all sales and purchases, cash receipts record keeping and stock control. It's also sound policy to review all purchases and expenditure from time to time and to ask tough questions. You should know all your suppliers, so you can spot fictitious ones. If staff know that there is surveillance of these areas, they will be less likely to take chances.
You can take out insurance cover to protect your business from the harmful effects of theft and burglary.