Perhaps, but all that would happen is that the negative score becomes smaller... if you have -50NP and the tax beast would come by, he would just take 5 NP "off", making it -45NP. Still not a desirable number
There is no 100% certain way to protect your items, but you can reduce it greatly by going directly to your inventory page and putting the item in your SDB. The only chance of stealing is when you go to your inventory. It's also useful to keep about 30 junk items, so they have a greater chance of picking that instead