Secure, yes, but against who or what ?
Regardless of how you encrypt data, your server must still be able to decrypt it. So any attack which subverts your server (e.g. buffer overflows or SQL injection) will yield full data access to the attacker, regardless of your encryption.
Encryption will do you any good only against attackers who get backdoor access to the storage, e.g. who steal a backup tape or recover an old hard disk from a dumpster. Then, this points to the kind of encryption you need: Transparent Data Encryption (equivalently, a full-disk encryption, as hinted at by @Polynomial). TDE does not remove confidentiality needs, but it concentrates them: you "just" have to worry about the encryption key, which is small and does not change over time, instead of gigabytes of ever-mutating data.
(Of course, if you want to sprinkle encryption all over the server just to ease the qualms of some administrative hierarchy somewhere, then forget all of this and just go for an algorithm with the most impressive-looking acronym, preferably with a very long key. "RSA-8192 and AES-256/CBC with HMAC/SHA-512" will reliably plunge the average bureaucrat into an ecstatic trance.)