It is amazing how this has not been thought up before it is a dog collar sure! However, built into it is a lead, it is so cool and great for those emergencies when the dog gets out. It is slightly on the expensive side but it has to be worth it, although the lead itself does not look to be that strong, a test may be required there!
These are the details for the Supercollar;
Supercollar® revolutionizes dog walking! The powerful collar with built-in three-foot retractable leash ensures you will never have to look for the leash again – it is always on. Super strength steel coated lead withstands 100s of pounds of tugging pressure, and is ideal for avoiding tripping or tangling experienced with other retractable leashes. Vet recommended for superior design, ease of use. Also features locking collar, walking reflectors and “D“ ring for traditional leashes. Polypropylene.
Priced at £25 in the UK or $40 in the USA
Source [Oh Gizmo]