  We use deep imaging from the Dark Energy Camera to explore the peripheral
regions of nine globular clusters in the outer halo of the Milky Way. Apart
from Whiting 1 and NGC 7492, which are projected against the Sagittarius
stream, we see no evidence for adjacent stellar populations to indicate any of
these clusters is associated with coherent tidal debris from a destroyed host
dwarf. We also find no evidence for tidal tails around any of the clusters in
our sample; however, both NGC 1904 and 6981 appear to possess outer envelopes.
Motivated by a slew of recent Gaia-based discoveries, we compile a sample of
clusters with robust detections of extra-tidal structure, and search for
correlations with orbital properties. While we observe that clusters with tidal
tails are typically on moderately or very eccentric orbits that are highly
inclined to the Galactic plane and often retrograde, these are neither
necessary nor sufficient conditions for the formation of extra-tidal structure.
That many objects with tidal tails appear to be accreted leads us to speculate
that this lack of consistency may stem from the inhomogeneous dynamical history
of the Milky Way globular cluster system. Finally, we note that clusters with
prominent stellar envelopes detected in ground-based imaging (such as NGC 1851
and 7089) are now all known from Gaia to possess long tidal tails --
experimental confirmation that the presence of an extended envelope is
indicative of tidal erosion.
