Garda band would be an anacronism in relation to the Tsar of Roosha who was executed in 1917 (allegedly). The Garda Siochana was formed in the 1920s after the creation of the Irish state. Hodnett would be bound to have known this, but the inclusion of both may well have been deliberate. I've often heard it sung as the Polis band, which could refer to the Dublin Metropolitan Police who I think also had their headquarters in the Phoenix Park.

Martin correctly points out that langers is Dublin slang for drunk, but your langer is also slang for the male appendage. I'll leave it up to you to decide which is intended.