With a command like "Leave It" , it is best to plan your teaching session. This means that you decide when you are going to teach it to your rottie.
First find 2 treats that your rottie likes. Then take the treats and your rottie over to a place
on the floor or to a low table like a coffee table.
Put one treat in your pocket and set the other on the floor or table right in front of your rottie's nose. As you set this treat down, you'll notice that your rottie is staring at it and drooling.
As you set it down, say, "Leeeave It" very slowly and firmly, but in a normal voice. Keep your hand right there. If your rottie leans in to get it, just cover it with your hand and repeat, "Leave It"
Wait just a few seconds, then grab the treat and praise your rottie wildly telling him
what a good rottie he is. Then, give him the second treat you have brought as a reward.
Don't give him the food he is learning on.
Repeat this game several times a day, just for a few minutes. As your rottie starts to understand
what "Leave It" means, you may begin to move your hand away just a little bit farther each time.
Eventually, you should be able to leave a treat on the table, sit in your chair, and be able to trust
that your rottie will leave it alone.