Bacteria and bacteriophages are locked in an arms race that exposes and exploits molecular vulnerabilities. Previously, we identified that sedentary chromosomal integrons (SCIs) of Vibrio parahaemolyticus are hot spots for antiviral immunity. These integrase-bearing elements can exceed 200 cassettes (up to ~5% of the genome) by integrating and excising environmentally acquired gene cassettes, ultimately generating rapidly reconfigurable libraries of adaptive functions. This previous work also identified two unannotated proteins with predicted DNA glycosylase folds that robustly defend against restriction-resistant phages carrying non-canonical guanosines (such as 7-deazaguanine); we term these defence-associated glycosylases Dag1 and Dag2. To chart the breadth of antiviral glycosylases in SCIs, we built a discovery pipeline coupling protein structure prediction with structural searches using FoldSeek. Using SCIs as antiviral hot spots, we assembled a protein-structure library of 76,370 proteins from 907 integrons across 1,094 non-redundant Vibrionaceae genomes. By searching with Dag1/2 predicted structures, we uncovered 109 unannotated glycosylase-like proteins that cluster into 24 highly divergent families (at <30% sequence identity, <80% pairwise protein coverage) yet retain conserved active-site architecture. Functionally, 17 candidates reduce/eliminate infection by guanosine-modified phages, indicating a conserved antiphage mechanism. Comparative genomics show that these glycosylases frequently co-occur with mobile elements, and are broadly distributed across multiple bacterial phyla. We propose that glycosylase-mediated excision of modified guanosines is a widespread and previously underappreciated strategy to unmask and dismantle chemically camouflaged phage genomes. Further, this work highlights a generalizable, structure-guided route to discover defence enzymes hidden in mobile genetic contexts.