I think seeing a qualified veterinary behaviorist or positive trainer who specializes in aggression is always your best bet.
but for what it's worth . . .
Block off the fences, all of them:
I think blocking the bassetts is good but I would also block the two males next door and/or visible access to the street and here's why: even if he is not reacting to them directly now, both could be creating barrier frustration which may be making him more reactive or increase his reactivity in future. It will help if you are out with him to re-direct any reaction and reward his non-reactive behavior, but the best situation for you to start working with him on his reactivity will be one where you can control all the variables. It doesn't have to be ugly. When we moved and we wanted to cover one of our fences (to prevent any barrier frustration before it even started) we picked up some willow fence from our local garden center and just laid it over the chain.
Many neutered male dogs develop inter-male aggression to entire dogs, it's really common. Other than desensitization there is not much you are going to be able to do to.
Shaping the absence (for this you will need an under control dog that Chase will react to):
What you are going to be working with here is your dog's flight distance. All animals have a radius of reactivity to a stimulus (with wild animals this radius is much larger). You need to find the edge of your dog's flight distance, this is where looking at body language will be helpful to you. Chaser will probably start signaling long before he is about to become reactive. The sweet spot will be where he can acknowledge the other dog he dislikes but still be responsive to you. Build up his non-reactive response slowly from this point by shaping the absence of the behavior you don't want: his reactivity. Every positive response (looking at you, looking at the other dog with no reaction, looking away or offering another calming signal) gets a reward (something reeeeeally yummy). Any negative reaction means you try to re-direct with a “watch me” until he stops reacting or move him back until he can focus on you again. Over a period of sessions you will try to decrease this distance until he can greet the other dog politely – obviously you should never move him directly toward the trigger, come in sideways, circling. If he wants to interact let him, but always try to end things on a positive note. Safe greeting and avoidance should be your expectation here, not sociability.
Here is a video of this procedure by Dr. Sophia Yin. Please note, as she says in her narration, she is using -R in the first demonstration because Podee is over-threshold. This is exactly what you don't want, dogs who are this aroused are incapable of learning. My personal preference is to achieve your focus without using a head halter - it disrupts a dog's body language and you really want your dog to be able to offer you their full attention without coercion - but it may be necessary if you are worried about your dog biting in excitement.
http://www.youtube.com/watch?v=EUCl6ndLN7Q
Chaser has hit adulthood, he may have decided that he does not want to interact with other male dogs, and that's ok. He needs to learn to exist with them when necessary, and to avoid when he would otherwise become reactive. Anything else is a bonus.
Depending on his drives, one strategy you could also try would be to work with him playing a focused game like fetch or doing obedience work he enjoys around his triggers (obviously not in a situation where the game could be interrupted, like the middle of the dog park). This will help him learn a positive avoidance of the things he doesn't like, teach him to focus on you, and build a better association with those triggers because they are the predictors of good things.
Playing fetch (a game she will perform any of her behaviors to initiate) around her triggers drastically improved our shiba-malinois' reactivity. However,
this will not work for every dog! It has the potential to make them more reactive if they get over-aroused by the game. It just boils down to what will work best for Chaser.
A word on NILIF
NILIF is a great tool, but it I think where you can run into problems is if you start utilizing it in the abstract. Your dog will never understand that they are allowed on the couch (for example) one day and not the next. They will, however, understand that there is an expectation of them if you start asking for a good behavior (like sit) before you invite them on the couch – or, if they are on the couch already, it could be asking for an “off” whose compliance is then rewarded with couch access. The point is not to earn privileges (privilege is a human construction, your dog does not understand “ I have been good all week so I am allowed on the couch now”) or remove access to resources until they “learn their place” but to have your dog offer good behavior for the things they want of their own accord. NILIF practiced this way will instil a level of self control in the dog and associate you with all of the resources they want.
Exercise (this one's more for LP, but they would work for for you too
One thing you could try with the bike would be to find yourself a springer (
http://www.springeramerica.com/). They were originally designed as shock absorbers for police officers in the UK to prevent their dogs from pulling their bikes off balance while on patrol. Also, if your dogs are pullers, you could consider investing in a few X-backs and a kicksled for next winter
. Seriously, its a lot of fun and a great workout for everybody (Moro is only about 35 pounds and she can pull me and the sled with no problem, but sometimes you have to run :P)
Two
books I think might really help
http://www.amazon.com/Click-Calm-Hea...5806333&sr=8-1
http://www.amazon.com/Fight-Practica...5806641&sr=1-1
Good luck