i want a guard dog but medium size?

Here below is a very informative link that will help you choose the breed that is perfect for you. Look under working dogs.

In response to the posts that have named any of the "pit bull" breeds:

While most pit bulls (or any breed that falls under this umbrella term) will protect their handlers within reasonable limits, they are NOT a dog that will defend property. The innate instinct to defend and protect property is not present in the pit bull breeds. Pit bulls act as more of a deterrent than anything else. Most have the "mean" look (even without ear cropping, they can still look pretty mean), and I would venture to say that someone who is ingorant enough to rob someone else's home probably buys into the stereotypes about pit bulls (a plus in that case for you!). Pit bulls will bark at any strange activity happening on the property, but will not denfend the property from strangers using force. Despite belief to the contrary, pit bulls are just too friendly with people, even strangers, to make effective guard dogs of property.

Just an FYI.

Do you know what a guard dog is? Is that what you are really looking for? A guard dog is a dog that will stop a human intruder by actually engaging him. It is not just an alarm dog, which is what most of the people here have suggested. Please understand the difference. Any dog can be an alarm dog, as long as he barks. Few dogs can be guard dogs as they will be required to bite a human and stop him. A good medium size guard dog is the malinois, some of he pit bull breeds, and maybe a smaller size shepherd. They are not cheap and they require a lot of training and work to own. Good luck.

I personally would recommend a Chinese Sharpei. They range between 45 - 55 pounds. They are very easy to house break, very intelligent, easy to train and truly loyal.

With this breed there is no training need for them to become guard dogs. When they mature it just comes naturally to them. They are very devoted to their family, but they are very stand offish with strangers. They will let you know when anything unusual is going on.

Also with this breed you must socialize them with people and other dogs. For example I have a male Sharpei that is a CGC (Canine Good Citizen) I take him to the Library 2 time a week, he loves kids and adults alike, but when we are home he will not let anyone in the house until I tell him that "they are friend".
I must advise you that they do have some inherit health problems, but if you get a good bloodline then they just require the usual one trip to the vet a year.
Good luck on what ever breed you choose.

Check out dogbreedinfo.com they provide a "breed test" and it matches you with the breed that fits you best.

a rottweiler (male) as they watch everything and are very sure to attack a robber. keep the tail as it looks better and helps the dog run as it acts like a rudder for when he runs around corners etc. do some research on the breed first.

Cockers, Pits, and Chows. however if you get a Chow or Pit be prepared to deal with an animal that some people are trying to outlaw in this country. However animals are just like kids, they can be taught to hate or to love, raise it right and you will have a faithful companion for life.

cocker spaniel,how about labs i have 1 they are very loyal 2 their masters

Beagles. They sound like terror when strangers come close to your house or property. The crooks will think you have a large dog in the house.

go to petfinder.com.......this is a site for rescue groups.......just enter your Zip code, and enter breed wanted, like Jack Russell Terrier aka Parson Russell Terrier, and be AMAZED at how many GREAT choices you have !!.......i recently adopted a Great Pyrenees mix from them, and my dog Sylvester is awesome !!.......check it out.......try it.......do a good deed.......adopt a Jack Russell Terrier today !!!.......good luck to you, in your search for a Jack Russell Terrier as a new pet !!!!.......most adoptions run between $ 50 to $ 200 maximum, for a wonderfull dog, who will be very happy to be your new pet !!!.......i adopted a large JRTerrier, wire-haired Terrier mix, and he is the greatest guard dog EVER !!,,he could be fast asleep on the couch, and he hears something, and wakes up and is out 2 doggie doors, running the perimeter of my back yard, or barking at the dining room window, at something going on in front of my home !!..he's also a great companion, and a very loving lap dog also !! ..i highly recommend a JRTerrier as a guard dog, and companion, and encouage you to check petfinder.com, for a GREAT selection of dogs, by breed !!!!