A hash is just one way to group things together in a unique ID.
The more elements the hash contains, the harder it is to break it. Reversing a hash will result in an attack on preimage, and the algorithm of the hash would be useless as you would have broken its main concept of hashing (not encrypting).
If everyone knows how the hash is calculated, anyone can fake the hash (In Bitcoin, everyone knows how it's calculated, because that's how the nodes can check if a hash is valid or not and thus know if the blockchain is changed has been). Apart from that, you may want to consider the secret of the hashing command to make it "safe."
Hash security itself is measured by how hard it is to break it. Sha256 is one of the most powerful hashes, since it is almost impossible to generate a pre-attack. However, if you want to make it more secure, you can hash the hash command. H (H1 (H0))
Where H0 is the first hash.
This would make it exponentially harder to break them (the more laps you use to hashing information, the harder it becomes an exponent number).
I hope that works for you to understand.