See if the local builders yard/merchant still sell 'Prompt cement' in small I think in 2lb bags. Check it suitable for the job. Drain pond is best way to go. However it may leak again as if the cement is deteriorating then further leaks will develop.
Think of a good quality butile liner. Take/send pond length and width to liner suppliers and you dont be suprised they double the length add a yard and same with width to allow for settling when filled with water.
In either case its best to drain it.
Bob, June 2011
