Security of web3.personal

Hello, i'm working on a Dapp and i want to be able to send transactions to my contracts.

I found how to do it but web3.personal.unlockAccount seems realy unsecure becaus another code could send transactions with the unlocked account during this time. How to lock back the account ? Is there a library which is safe to use to sign and send transaction ?

I saw there is a personal.lockAccount in geth but i cant see it in my browser i don't know why (when i can see personal.unlockAccount)