  We revisit constraints on decaying very heavy dark matter (VHDM) using the
latest ultrahigh-energy cosmic-ray (UHECR; $E\gtrsim 10^{18}$ eV) data and
ultrahigh-energy (UHE) $\gamma$-ray flux upper limits, measured by the Pierre
Auger Observatory. We present updated limits on the VHDM lifetime ($\tau_\chi$)
for masses up to $\sim10^{15}$~GeV, considering decay into quarks, leptons, and
massive bosons. In particular, we consider not only the UHECR spectrum but
their composition data that favors heavier nuclei. Such a combined analysis
improves the limits at $\lesssim 10^{12}$ GeV because VHDM decay does not
produce UHECR nuclei. We also show that the constraints from the UHE
$\gamma$-ray upper limits are $\sim10$ more stringent than that obtained from
cosmic rays, for all of the Standard Model final states we consider. The latter
improves our limits to VHDM lifetime by a factor of two for dark matter mass
$\gtrsim10^{12}$ GeV.
