The dip is one of the best bodyweight exercises for developing the shoulders, chest, and triceps, but it's certainly not for everyone. Larger people, those with less relative body strength, or those who have pre-existing shoulder issues may struggle with regular dips.
If you're looking for a safe alternative that delivers similar benefits without as much stress on your shoulders, try this.
This exercise stimulates the lower fibers of the chest, much like a decline bench press, but it takes very little setup time. Reversing your grip on the bar will allow you to get more triceps activation, and it'll act as a protective mechanism for your shoulders because it'll prevent your elbows from flaring out.
Although you could do this from a box, I prefer a barbell because it's more comfortable on the wrists and it'll be easier to gradually increase the difficulty. Lowering the bar down another inch or two on the J-hooks is significantly easier than jumping from an 18-inch box to a 12-inch box.
Think "stretch the bar" as you're pressing up. This will activate your lats and help maximize the tension you feel in the pecs and triceps at the top of the push-up.
To increase the difficulty, lock your core into a hollow body position with your hips slightly elevated. Try to touch your lower abdomen or waist to the bar instead of your lower chest. This will put you in a rounded upper back position, but this is actually ideal as long as your hips stay level and your core stays engaged.