Nothing is 100% secure. For example, EEPROM and flash can be read using techniques like Scanning Probe Microscopy & Scanning Electron Microscope, even if the security bit is set. IMO, the goal to safely securing your data is to make it extremely hard. You should take a look at the ATAES132a from MicroChip.
The first device in the AES family, the ATAES132A, is a high-speed, high-security, 32K Serial EEPROM that enables authentication and confidential nonvolatile data storage
It also boast a tamper resistant hardware
The ATAES132A device contains physical security features to prevent an attacker from determining the
internal secrets. ATAES132A includes tamper detectors for voltage, temperature, frequency, and light, as
well as an active metal shield over the circuitry, internal memory encryption, and other various features.
The ATAES132A physical design and cryptographic protocol are designed to prevent or significantly
complicate most algorithmic, timing, and side-channel attacks.