Ah yes, "The Backup Plan". The demoralizing question you will be asked by almost every resident as you make your way through the audition process. Before considering TBUP (?), carefully consider your approach this season and understand that your odds of obtaining a spot are much better on your first swing at bat. Also, DO Uro seems to favor the "completeness" of an application (scores + letters + research + rotation performance). Give this all you've got and try to do away rotations to gain exposure to a good number of the available spots.
I applied to Gen Surg and pursued the possibility of doing a research year if I did not match.
Gen Surg: For me, I originally thought GS would be a good TBUP. I enjoyed GS and really like the big open procedures in Uro (RPLND, open partial Nephro). I did a solid GS Sub-I and went on a bunch of GS interviews. In the end, I was completely honest with myself and admitted that while I may enjoy the GS training, I did not want to spend my life as a GS. I ended up ranking only uro programs after getting good feedback, going on many uro interviews, and having a strong feeling I would match DO Uro. You need to also realize the risk of not ranking a backup speciality needs to be very personal and calculated. Don't take this risk just bc it worked out for someone on SDN.
Also, be careful of using other specialities, esp surgical/competitive, as back-ups. The residents and PDs will be offended if they discover such. I was honest on my GS Sub-I, but do not advertise TBUP to anyone.
Research: Uro programs are quite receptive to applicants with robust research backgrounds. I felt if I took a year off to do some meaningful Uro research and published first author, that I would bring some unique qualities to the table if a re-app was necessary. But, beware that some programs may not particularly seek out a re-app with non-clinical experience in the gap year (ie Lansing). Again, this is a personal decision.
TRI: I think TRIs can be beneficial under the right circumstances. IMO, I think TRIs at institutions which have a home DO Uro program seem optimal. In this year, I would try to get face time with the programs residents and PDs, assist on cases after-hours/weekends, and try to latch on to a research project with the residents. I think the main idea is to be at a Uro institution. There are a lot of TRIs that will promise people who failed to match competitive residencies (Uro, derm, optho, ortho) outcomes, but I think they are largely trying to obtain cheap labor from people who are very well-qualified.
Pre-lim Surg at an MD GS Program: I'm not a big fan of this option. Mainly bc the time spent here does not count as a DO intern year- unless I am missing something. I suppose if you were gunning for an MD uro spot it could make sense. But, if you were a DO who was competitive for an MD Uro spot I doubt you would be giving things a second shot.
The theme: it has to be a personal decision tailored to your personal goals. Be honest with yourself regarding your career and your strength as an applicant.
Don't overthink things, give this all you've got, and, most importantly, have faith in your abilities. You will have many long days, may find yourself driving across the country for an away thinking "This is nuts", and you will certainly have TBUP conversation many times over- but I promise you it is worth it.
Good luck and I hope to see you on the wards.