The method for sealing the pond really depends on the geology of your site. What is the parent material? Is there a flow of water
? Is this in a key point? Is there a natural clay layer?
The most regenerative would be to build a key way dam at the key point of a valley, tied into the parent clay layer. This provides the most water stored per cubic foot of earth moved. How big is your catchment and what is your precipitation and evaporation? Pigs do a great job
making ponds but they won't be able to seal sand. What resources are readily available? Ducks certainly help seal up a body of water as well, but do their best work in very shallow water.
The hugelkultur could certainly work but again this is situation dependent. Without knowing your climate and geology I would just be making up a situation in my head to answer
with any more detail. Can the overburden be used to create a berm to shelter
growing areas from the harshest weather?
Hugelkultur is often treated as a modular permaculture
solution for all properties, but this is just not the case. I have been involved with 7 sites that Sepp has visited in North America, only 2 has he recommended Hugelkultur for the project
. Hugelkulturs have been created at more workshops than those two but most just because of the demand from the students and the limits on the landowner to do anything else.