Although everyone is aware of the danger that open water poses to children it's not just them that need to be considered; the edging and surroundings need to be safe - be aware of raised stone paving (a tripping hazard), water that has splashed out of your pond from your waterfall can be slippery and in winter can freeze.

Please be aware of outdoor electrics and that electricity and water do not mix well. Always use a circuit breaker system and go through a properly earthed fuse box. If running any length of cable underground it should be armoured and buried to a depth of at least 1 metre. If in any doubt consult a qualified electrician.

Finally, give some thought to the physical side of building; you will be moving and lifting heavy and often unwieldy materals for example concrete blocks, excavating soil and perhaps railway sleepers. You may also be using equipment you haven't much experience with such as concrete mixers, sthil saws and angle grinders as well as ones you might be more familar with; saws, hammers, stanley knives. Ensure that you wear appropriate clothing and footwear and be aware of your own body's limitations - don't put your back out.