I'm no structural engineer, so others may be able to advise more accurately. Land support around is certainly important however I think the issue will be that if the pond fills during rainy season but then empties during the dry the changes in pressure on the concrete can cause it to break. The guy building my Pool was a structural engineer in the UK prior to Thailand. If you like I can pm you his number. If you give him the dimensions I'm sure he can quickly work out steel and concrete requirements to ensure longevity.