The answer does not seem to be showing. Here it is again.
I am giving you the answers and I'm not sure why you think these answers are simple. It takes a lot of work and time to train a dog but it is important or a dog will take advantage of the owner. It is that simple. Those sites also support the answer I am supplying you. Most customers appreciate links to sites that support the answer they are receiving. I refer you to other sites that give excellent ways of training dogs so you don't have to pay a professional trainer to come to your home to train your dog. You could choose that option.
However, a dog respects the person training them. If someone else trains your dog, then your dog may respect them and listen to them, but still see you as lower in the pack and someone they can bite when you don't do what they say.
The Nothing in Life is free program just requires that you make the dog do something in order to get the things he needs such as food, attention, treats even play time. It can be as simple as making him sit before petting him, but it establishes him as the lower pack member and you as the boss.
The leave it command teaches a dog to give up what it has. The site I gave you goes over it in detail and I also wish the site allowed me to put links in to make it easier to refer you there. Here I will include the instructions on their page here for you.
"To teach the command you will need plenty of small treats, something your dog really likes, no larger than a quarter of an inch square. (Avoid treats with a high salt or sugar content.) Keep your sessions short, no more than five minutes at a time. Make yourself comfortable – sit on a chair or the floor, depending on the size of your dog, and you are ready to start.
Sequence 1: Hold the treat between your thumb and index finger. With your palm facing up, get your dog interested in the treat. When he tries to pry the treat out of your hand, say “Leave It,” close your hand into a fist, and turn it so that your palm now faces down. Observe your dog’s reaction. He may stare fixedly at the back of your hand, he may try to get to the treat by nuzzling or nibbling your hand, or he may start barking. Ignore all these behaviors and do not repeat the command. You’re looking for the first break in his attention away from your hand. He may look away or make eye contact with you. When he does, say “Good,” and give him the treat. The trick is to watch his eyes and the instant he even glances away from your hand, praise with “Good” and reward with a the treat. Repeat until your dog looks at you or away from your hand when you give the command and turn your hand over.
To find out whether your dog is responding to the command or to the turning of your hand, repeat the beginning sequence without turning your hand. If he responds, praise and reward. If he doesn’t, close your hand into a fist around the treat and wait for the break in attention. Repeat until he responds to the command.
Sequence 2: Show your dog a treat, put it on the floor, and cover it with your hand. When his attention is on your hand or he tries to get to the treat, say “Leave It.” Wait for the break in attention, and then praise and reward. Now cover the treat with just your index finger. Then try it with placing the treat between your index and middle finger. When your dog reliably ignores the treat on command, place the treat 1 inch in front of your hand. Here you need to be watchful: He may be faster at getting to the treat than you can cover it. If he does, no harm done, just try again and be a little more watchful.
Sequence 3: Put your dog on leash and stand next to him (heel position). Neatly fold the leash into your left hand, and hold your hand as close to his collar as is comfortable without any tension on the leash. You need to make sure that the amount of slack in the leash isn’t so much that his mouth can reach the floor. Hold the treat in your right hand and show it to your dog, and then casually drop the treat. When he tries to get to the treat, say “Leave It”.
If he ignores the treat, praise, pick up the treat, and give it to him. You want to teach your dog not to pick up something of the ground on command, so you must always pick up the treat and then give it to him. If he tries to pick up the treat, pull up on the leash so he can’t get to it. Remember, the object is to bring the dog’s attention back to you, away from an object that attracts him, so you can reward your dog. Repeat until he obeys the command.
Sequence 4: You are now ready to test his response to the command off leash. With your dog sitting at your side, show him the treat and then drop it in front of him. As his eyes follow the treat, say “Leave It”. If he makes a dive for it, don’t attempt to beat him to it or yell “No.” He’s telling you he needs more work on leash. When he reliably responds to the command off leash, you can advance to your ultimate goal – finding something potentially edible on the ground. "
I also do not see how it is so difficult to pick up a simple bell of any size shape, etc, attach it to a string and hang it from the door know. A simple push on the string should ring it enough for your dog to make the connection.
Unfortunately, I'm not there in person to help you train your dog and thus can not do the work for you. I do hope you make some changes before you find your dog becoming even more aggressive. The breed is known to have aggression issues and he is reaching sexual maturity and testing his boundaries with you. Without you training him, he will just become more out of control, but it is your choice whether you are the one in charge or he is.
I also want to mention that an in person trainer or behaviorist most likely would charge twice this for one session. This issue would also take multiple sessions over weeks or even months as I'm sure you will find when you explore in person options that are available.
Jane Lefler and other Dog Training Specialists are ready to help you