Dog breeds vary in their tendency towards separation anxiety. The Sussex Spaniel is a breed that is predisposed to suffer separation anxiety more than other breeds. This may be due to its role as being part of the hunt and a pack of dogs. When it is separated from this pack, it tends to bond with its owner. If the owner doesn't understand the dog's needs, it can lead to the dog displaying negative behavior like destructive chewing and barking. It will even howl when it is distressed. Some dogs with soil the house, if left alone too long. This might be because they missed their outing or because they are angry or upset. Don't discipline the dog for these mistakes as it is acting out of distress that you were gone. Instead, try to develop a routine that is comforting to the dog while allowing you some time away from the home for short periods. The best type of environment for a Sussex Spaniel is one where there is someone home all day long.
A well-socialized dog may be less prone to separation anxiety than one that has been isolated too early from its mother or brought up in a kennel. Still, you cannot leave these dogs alone for too long. They will never really be able to withstand long periods of isolation. If you are someone that works outside the home, then this may not be the breed for you. On top of requiring some companionship, the dog also needs to be exercised regularly and vigorously. If you don't have the time to be with this dog, then a different breed might be more suitable for you.
One of the things that you can do to help your dog overcome some of its tendency to be upset when you are gone is to get it obedience training. This will help you understand the mind of the dog and why it behaves the way it does. There are some human personalities that can make the dog more needy than it actually is, by pampering the dog and developing too much of an emotional connection. If the dog is following you around from room to room, it may have developed this type of emotional connection and you need to start paying less attention to the dog while you are in the house. This will make it easier when you choose to leave the house to get it to behave.
Have a gradual program of withdrawing your presence from the dog little by little. It can become used to some periods of time without you, if it knows that you are slated to come back shortly. The Sussex Spaniel is one of the dogs that will always have a tendency to feel separation anxiety, but with the proper upbringing, socialization, and training the destructive behaviors can be minimized.