Dog lead restraining it? No lead to pull – tire out bagging mess up (3,4,7)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

A charade of PITB, an envelope (‘restraining’) of ‘it’ in PB (chemical symbol, ‘lead’) plus ‘[p]ull’ minus its first letter (‘no lead’ – different pronounciation) plus TERRIER, an envelope (‘bagging’) of ERR (‘ness up’) in TIER, an anagram (‘pout’) of ‘tire’.