In addition to setting a contingency per cent set as a control when planning, there needs to be measurable controls as well to stay within the budget throughout the period and check for extra expenses if it occurs. Controlling a budget could be done through assigning responsibilities for a specific amount of the budget to an accountable that overlooks the operations and its spendings, requiring an approval for spendings that are higher than x amount of money, allowing access to the budget only to certain employees, documenting each transaction, set budget KPIs etc.