Hey Fish -
Like Corsair suggested, riding at lunch is an option. I checked your stable on the "Getting to Know you" thread, and it says you don't have a road bike. If the dogs are that big of a threat to you (you DO have to take that seriously, unfortunately), get yourself a portable trainer (I have a Cyclops Fluid), set yourself up on that, and ride. You can use mountain bikes on them too (just use slicks).
Granted, you don't exactly go anywhere, but you'll still reap the benefits of the fitness gained or maintained. That's actually what I do -- I'm in a similar situation as you. My kids are 8, 5, and 3 (as of today! My baby's 3!), and I get the "mommy's home" mob when I get home, and then I'm pulled from the trainer for baths, tuck-in's, "cuddle with mom" time, etc. and don't get all the trainer time I need. A way to gain back that time is to bring the trainer to work (I keep a spare bike there). I can ride just long enough to get the heart rate up, do some intervals, and get a good sweat going before I have to stop. We have a shower room downstairs, but wet wipes would work just as well to freshen up if you don't have access to a shower.
You're fortunate that your husband rides, so he understands the joy you get from riding, and that he is willing to watch the kids for you when you go out solo. Please do not feel as though you're being selfish, though -- and believe me, I understand exactly what you mean. With all the demands we woman are under these days, holding down responsible jobs (yours is cool!), keeping up the house, raising the kids, handling the finances, planning the birthday parties, and lots more, we need moments in our lives that are just OURS, ones that refresh our soul and lets us be ourselves. Like I said, you're lucky that your husband understands that and supports you. You should NOT feel guilty for what you need to be YOU, an individual, with no labels attached (i.e. mom & wife). You need YOU time.
Good luck and have fun!
~BikeMomma
"Only two things are infinite, the universe and human stupidity, and I'm not sure about the former." --Albert Einstein