Mark, it sounds like you've got a pretty good first line of defense with the dogs and the lights. If the police are slow to respond you might consider a good handheld spotlight and a video camera to document the situation.
Regarding buying a gun..........in a life-threatening situation, it's a deadly force last line of defense solution. I own several, and have used guns for hunting for over 40 years. However, unless everyone in the home is well acquainted with a firearm, it can become a slippery slope quickly if used to defend your home and family. A clear and present danger has to be established before the trigger is pulled, and after it is, there's no going back.
It makes a huge difference depending the situation you're dealing with.
Please think that through (although I imagine you have already) before making a decision.
I'll stop now before I get into a political discussion. I'm sure I'll get flamed from both sides, but using a gun for defense is a very serious matter, period.
Guitars
Wilburn Versatare, '52 FrankenTele(Fender licensed parts), Fender USA Roadhouse Strat, Fender USA Standard B-bender Telecaster, Agile AL 3000 w/ WCR pickups, Ibanez MIJ V300 Acoustic, Squier Precision Bass,
Amps
Ceriatone Overtone Special, Musicman 212 Sixty-Five, Fender Blues Jr., Peavey Classic 30, Fender Super Reverb, Traynor YCV-40 WR Anniversary w/ matching 1x12 ext. cab, Epiphone SoCal 50w head w/ matching 4x12 cab (Lady Luck speakers), Avatar 2x12 semi-open back cab w/ Celestion speakers
Pedals
Digitech Bad Monkey, Digitech Jamman, DVM's ZYS, Goodrich volume pedal