should I create a shallower shoreline?

Wildlife ponds should have sloping sides.

The Pacific Tree Frogs like my clay wildlife pond with sloping sides. In
the evening they hop to the waterline and sit half in and half out of the
water as they croak.

I believe the pond loses very little water through the clay bottom. The
minimal seepage through the bottom probably helps keep the pond clean and
the mineral build-up down...no need to change out water.

The clay pond does lose more water than my preforms in the summer
time....it is a chore keeping all of them filled in the summer...small
advantage here to the plastic ponds. The clay pond loses more water in the
warmer months due to the wicking of water to the dirt above at the
waterline. I don't think a liner on the bottom is necessary if you have
clay soil...however a liner at the waterline would help reduce the wicking
action. Perhaps rocks would work instead of the liner at the water's edge.

I use the sprinkler system to keep the clay pond filled.