Small garden implement — what could be about a foot (4)
I believe the answer is:
shoe
'what could be about a foot' is the definition.
(shoes are worn on the feet)
'small garden implement' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'garden implement' becomes 'hoe' (tool used when gardening).
's'+'hoe'='SHOE'
(Other definitions for shoe that I've seen before include "Sandal or brogue?" , "Last product" , "Eg, brogue" , "eg Trainer" , "Pump, for example" .)