preformed pond help and other gardening tips

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' (http://tinyurl.com/cqzucjh)

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'
(http://tinyurl.com/chwwc2r)
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.




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CHS_87