There are a number of breeds that can easily do this. There are mixed breeds that can as well. I will not recommend a specific dog breed. When that is done it is because of our person prejudice and preferences. If I recall correctly you have pit bulls. If that is correct they are more than able to do the work. Even though they weren't red to guardians they can and do excel in it when taught.

This is the problem I have with what you are asking. Please don't take this the wrong way. I mean no harm. You are going about this the wrong way or the wrong way of thinking. Of course you already know i;m a strong advocate of proper training if you want a good guard dog. The statement that I have a problem with is that you want them dead. You want them caught and basically killed before they get over the fence.

My personal preference if for them to never step a foot onto my property. My dogs accomplish this well. But lets say you take it the way that you said. You are going to end up in court. You are going to have a huge bill for lawyers. There is a good chance that you dogs will be put to sleep and you will be fined and charged. You may end up in jail and prison. Most laws will not favor you. In our minds they are trespassing. Yes they are. But the law will look at you as having premeditated having viscous dogs that are a danger to the community. They will likely throw the book at you. You will feel that you have been wronged.

Not only do I have dogs and train dogs for personal protection. I also teach martial arts. I don't teach it for sport. I can and I have But I teach it for self defense but more towards life preservation. The intent and tactics are different for competing and for life preservation. Self defense is actually a legal term that we often use incorrectly in terms or martial arts. Most people that rain or don't train will say statements similar to yours in regards to "self defense". I even have a student that I had to talk to about this thinking he should know better. He was working do repossessions. He and a co-worker found a car they were looking to repossess. While doing this the owner who is behind on their payments came out and tried to stop them. Apparently she got in the car and may have tried to hit one of the guys. My student for some unknown reason jumped on the car while it was moving.  Now holding on for his life. The police shows up. I don't recall the order in which they came. She stops the car. She gets out. He shoves her. He's mad. The police asked them do they want to let her go with the car or keep the car and get a ticket for assault. In his mind his shove was in self defense because she tried to hit them with the car. I tried to explain it to him the law says you can only do so much in self defense and when it warrants it This was no longer self defense because she was no longer trying to hit them. She stopped the car and got out of it. Basically she was no longer a threat. If she was attacking them they can use force to stop her. But she wasn't threatening. The police did them a favor by not charging them. If I walked up to you and punched you in the nose. Then I begin to run away. You chase me and beat me up. That is not self defense. That is assault. I'm not threatening you. I'm fleeing. The same thing with the dog. They are fleeing. They are no longer a threat. 

I'd rather tell you the truth than for you to find yourself in a bad situation and end up in jail or prison.

My suggestion is to have well trained dogs. Dogs that are intimidating enough to keep most intruders out. Use females dogs. Not because they are better at guarding. Some females are. But I don't believe all females are. Sure males ore being and often more intimidating. While I believe there is some truth to hell has no fury like a woman scorn, but that is not the reason. If you have intact males. The would be thief might use something that most intact males can't on won't resist. They bring a female dog in heat. In martial arts we teach for worst case scenario. That is worst case scenario. It is unlikely to happen. But it can. I would say for it to happen it would more likely happen to very high end homes of the very wealthy and and or famous. Not so much the average person. They have a female in heat and open the gate and send her down the street. The male is going to try to breed her.

This well trained dog should be taught food/drink refusal. Not to take food from strangers. Not to take food that is lying around. This keeps them from being poisoned.

With all of that being said. If you need that much security and they want in your space bad enough they will still get in. You might need motion sensor cameras that are monitored by the police department or your armed security firm.