The cargo nets are pretty cheap. May be able to find them at some parts stores, but I know for sure walmart carries them. I saw them today for about $6, but then again I live in Ky and prices may vary. I use these often. Comes in very handy!

As for protecting from thieves...be sure to keep the bike in easy to see areas and some bikes may have a lock on the front that keeps the front wheel/handle bars from turning. probably not really going to keep it from being stolen since the bike is 400lbs or less lol. The most effective security is to purchase/install an alarm system. \

I don't personally have one but have heard of scorpio systems. Google will be your friend here. here is a link for at least the scorpio systems.....
Scorpio Alarms » Motorcycle Products
If you have any other questions feel free to ask!