Identity-first composition. The design has to read as snail-dad first, generic-animal-shirt second. A single shell silhouette or a centred illustration can do this; a busy collage usually cannot.
Print legibility from across a room. Father's Day means family photos, garden gatherings, and group dinners. Designs with clear central artwork and high contrast between motif and shirt colour read better at three metres than fine-line styles that disappear in distance.
Crossover with his other interests. A snail dad who also cycles or hikes responds to designs that fuse both worlds. These crossover prints do double duty: niche-identity on the surface, activity-cue underneath, so the t-shirt slots into more than one weekend wardrobe.
Father's Day timing. The third Sunday in June leaves a tight window. Place the order in the first week of June to leave room for any second-guessing before the Sunday itself. If the choice falls on larger sizes (2XL and up), start a few days earlier on top of that.
Wearer-fit over novelty. A snail dad gift that lives in the back of the drawer is a failed gift. Designs that look at home with the rest of a casual rotation, jeans and a quarter-zip, earth tones, weekend-garden uniform, get worn beyond the actual occasion. Bright novelty prints tend to come out twice and then retire.