Weapon to keep animals together outside a pound (7)
I believe the answer is:
halberd
'weapon' is the definition.
(halberd is a kind of weapon)
'keep animals together outside a pound' is the wordplay.
'keep animals together' becomes 'herd' (I can't explain this - if you can you should give a lot more credence to this answer).
'outside' is an insertion indicator (some letters go outside others).
'pound' becomes 'lb' (abbreviation for the unit of weight).
'a'+'lb'='alb'
'herd' placed around 'alb' is 'HALBERD'.
'to' is the link.
Can you help me to learn more?
(Other definitions for halberd that I've seen before include "Ancient battle-axe" , "Ancient weapon" , "Sharp instrument" , "Combined spear and battleaxe" , "Old weapon" .)