For me, there are several decent choices. I am not into modding, but as retired LEO, I have carried lights for over 30 years. My favorite seem to be Streamlight rechargeables. Great amount of light, almost unbeatable throw with good spill. The SL20X LED is the best of both worlds: LED for long runtime and good flood-type light, yet still has the incandescent for great throw. It is not cheap, so may be outside of your budget.
My suggestion for you would be a Surefire G2. List is $36.00, it is made of Nitrolon (some kind of fancy, really tough plastic type material), not too heavy, and it puts out great light. The throw for such a small light is very good, and you get some spill, enough to walk with while lighting up the path ahead. After you have learned a little more about lights, you will be in a position to make a more inform purchase to fulfill your needs. You can then put your G2 in the car. The lithium batteries will last quite a long time in storage, and if you need a light while you are out, it will be there and will work.
I have used my Streamlights for more than just illumination on several occasions. They have never failed. My first was an SL35 in 1980 or so. I still have it. If you plan on using your light as a potential defensive weapon, learn a little about how to use it. A blow to the head is difficult to land, can be fatal and has the potential to leave you vulnerable to attack. LEO's are taught to use one level of force above their attacker: If the bad guy has a stick, use a gun. If he has hands, use a baton. If you stay with in those guidelines, I suspect you will have a very defensible position if it becomes an issue. Pepper spray is pretty good. Just be prepared for the wind to blow at least some of it back in your face. To use a hand held stun gun-type device, you have to be within an arms reach, which is much closer than I prefer.
I like your idea of letting Rover take care of business if at all possible. Use your light to make sure he can see where to bite next.
What ever you do, if you get into a self defense situation, if you are fortunate enough to get clear of it, CALL THE POLICE AT YOUR VERY FIRST SAFE OPPORTUNITY, even if the bad guy gets away. If yo go home, and the bad guy calls about your dog attacking him while he was walking and minding his own business, you may lose in court. Be the first to call. And don't forget to call an ambulance to help your assailant. Helps to show you did not want to hurt him, you had to in order to protect yourself.
