Concecrated ground gives aegis 1. Shallow sea makes non aquatic creatures roll 1 less die. The combined effect is quite like aegis 2
The problem with this is that both are terrain. If you put one down in a zone, then the other would replace it if you cast it.
The card people are trying to combine with Shallow Sea is this one: [mwcard=MW1E37]Sacred Ground[/mwcard]
Not Consecrated Ground. So yes,
SACRED GROUND can be combined with Shallow Sea to get an effective "Aegis 2" against Melee attacks.
Consecrated Ground and Shallow Sea are two terrain cards that cannot exist in the same zone simultaneously. Nor does Consecrated Ground actually do anything with Aegis.