Agree...just make sure your rocks, your waterfall and weir have a liner under it. The liner should be pitched toward the pond and concave shaped so that if any water gets around, under or over the rocks, it can only go one place...back down into the pond.
If your liner isn't big enough, you can add another liner to the pond liner, just make sure it fully overlaps the pond liner.
About cutting the hose...I guess it depends on what type of hose it is. Most will be OK, but some of those corrugated hoses have specific ends for using hose clamps. What type of hose is it? Can you post a picture?