Good day!

Recently, I have received on one of my wallets 50 satoshis payment from an unknown address, which might be used to find out my other Bitcoin addresses if I spend them. I am using Bitcoin-Qt for the address that received the payment.

My question is the following:

Provided I keep my payments are always rounded to 5 digit can I guarantee that those 50 satoshis transaction never gets spent?

Are there any other ways to isolate these coins, maybe send them specifically to another address?