hi, people. i'm new to this so i don't know if i'm in the right place and if so if you could point me in the right direction, that would be helpful.

anyway, i have installed a preformed pond. i've put the water in but yesterday realized the soil around it was sinking so i flattened it, added more soil and repeated to build it up. the pond is a lotus preformed pond the capacity is 1200 litres. i have this filter/pump in mind:
eBay - The UK's Online Marketplace

the reason i have come on here is to ask this: the cable comes with 5m of cable and i need at least 10m. can i buy an outside extension cable like this, eBay - The UK's Online Marketplace
and plug the it in and tack the wire underneath my bamboo wall fencing? i don't really wanna dig and wrap in pipe as it means digging again.

also, any general tips on keeping cats out the garden, time before putting fish in, do i use pebbles on the bottom? many thanks.