Eliminate DTM spikes

Eliminating "0" spikes in your DTM's
Select your surface and select "Surface Properties",

Select the "Definition" Tab,
Expand "Build",
Find the variable that says “Exclude elevations less than” and set it to YES,
Directly under that find the variable that says “Elevation”, set that to 1.
Select Apply, OK
This will keep your surface from spiking to "0" elevations (or worse NEGATIVE).