public void ProcessOrder(Order order)
    {
    	Guard.Against.Null(order, nameof(order));

        // process order here
    }

    // OR

    public class Order
    {
        private string _name;
        private int _quantity;
        private long _max;
        private decimal _unitPrice;
        private DateTime _dateCreated;

        public Order(string name, int quantity, long max, decimal unitPrice, DateTime dateCreated)
        {
            _name = Guard.Against.NullOrWhiteSpace(name, nameof(name));
            _quantity = Guard.Against.NegativeOrZero(quantity, nameof(quantity));
            _max = Guard.Against.Zero(max, nameof(max));
            _unitPrice = Guard.Against.Negative(unitPrice, nameof(unitPrice));
            _dateCreated = Guard.Against.OutOfSQLDateRange(dateCreated, nameof(dateCreated));
        }
    }

    // Using the same namespace will make sure your code picks up your 
    // extensions no matter where they are in your codebase.
    namespace Ardalis.GuardClauses
    {
        public static class FooGuard
        {
            public static void Foo(this IGuardClause guardClause, string input, string parameterName)
            {
                if (input?.ToLower() == "foo")
                    throw new ArgumentException("Should not have been foo!", parameterName);
            }
        }
    }

    // Usage
    public void SomeMethod(string something)
    {
        Guard.Against.Foo(something, nameof(something));
    }