  The synthesis of $r$-process elements is known to involve extremely energetic
explosions. At the same time, recent observations find significant $r$-process
enrichment even in extremely small ultra-faint dwarf (UFD) galaxies. This
raises the question of retainment of those elements within their hosts. We
estimate the retainment fraction and find that it is large $\sim 0.9$, unless
the $r$-process event is very energetic ($\gtrsim 10^{52}$erg) and / or the
host has lost a large fraction of its gas prior to the event. We estimate the
$r$-process mass per event and rate as implied by abundances in UFDs, taking
into account imperfect retainment and different models of UFD evolution. The
results are consistent with previous estimates (Beniamini et al. 2016) and with
the constraints from the recently detected macronova accompanying a neutron
star merger (GW170817). We also estimate the distribution of abundances
predicted by these models. We find that $\sim 0.07$ of UFDs should have
$r$-process enrichment. The results are consistent with both the mean values
and the fluctuations of [Eu/Fe] in galactic metal poor stars, supporting the
possibility that UFDs are the main 'building blocks' of the galactic halo
population.
