Encostalar literally means "to put in a sack" or "to bag something." It's an unusual and striking verb that immediately grabs attention because it's not a common word you'd expect in a song about love or relationships.
In "El Gallito," the singer's wife warns him, "Que me van a encostalar" (that they are going to put me in a sack). This phrase is a colorful, colloquial threat implying that if he's not careful with other women, he'll end up in serious trouble, possibly even dead or severely harmed, and disposed of like trash. It adds a dark, humorous, and very memorable twist to the lyrics.
"El Gallito" leans on a classic ranchero image: the singer compares himself to a rooster kept penned up with the hens, tied by the leg so he can't stray. His wife would rather see him grow old at home than let him "breed" around, and he plays the line for both humor and a little self-pity, admitting he doesn't know what to do about it.
Midway through, the song breaks from the love story for a shoutout: "para todos los galleros de Navojoa," a dedication to cockfighting breeders and fans from Navojoa, Sonora, plus a nod to a specific "comandante." That kind of on-record dedication is common in regional Mexican music, where a corrido or norteño track doubles as a message to real people and places back home.
It's a song about feeling cornered in a relationship, dressed up in the rooster-pen metaphor the title promises.