The EDNS0_UL (Update Lease) (draft RFC) option is used to tell the server to set an expiration on an update RR. This is helpful for clients that cannot clean up after themselves. This is a draft RFC and more information can be found at

o := new(dns.OPT)
o.Hdr.Name = "."
o.Hdr.Rrtype = dns.TypeOPT
e := new(dns.EDNS0_UL)
e.Code = dns.EDNS0UL
e.Lease = 120 // in seconds
o.Option = append(o.Option, e)

EDNS0_UL is referenced in 1 repository