It is disputed amongst the Poskim as to whether there is an intrinsic prohibition against entering a dog into a shul, with the Rebbe taking a lenient approach in the event that the person cannot go to shul otherwise, such as he needs a service dog, or a guide dog for blindness. However, certainly one is not to bring his pet dog into the Shul without the above reasons of necessity due to the above debate and due to the fact it may be a disturbance to the public. Likewise, even by a service dog, the shul management is to consider the effect that having the service dog present will have on the other congregants and mitigate a solution that will make everyone happy.

See: Poskim who prohibit: Torah Shleima 15:147; Chelkas Yaakov 1:34; Yalkut Yosef 151:25; Shema Shlomo 4:3; Mikveh Mayim 5:19; Mishneh Yosef 9:53; See Michaber 153:21; Sifri Ki Seitzei 281; Keli Yakar Ki Seitzei 23:19; Chinuch Mitzvah 571 Poskim who permit: Rebbe in Igros Kodesh 18:422 and 455, printed in Shulchan Menachem 1:113; Igros Moshe 1:45; Daas Noteh Teshuvah 68; See; Ran and Ramban on Megillah 28a in name of Yerushalmi Megillah 3:3

I had a $1000 debt to my local Kosher grocery shop who allows me to buy on credit and was unable to pay him back and therefore was not able to buy anymore products from the store. I mentioned my problem to a few friends, and lo and behold the next day the grocery store owner tells me that the debt has been paid in full by an anonymous individual. This happened over two years ago and I am now more financially stable and would like to know if I am obligated to pay this person back.

Answer:

You do not have to pay him back, even if he asks for the money back, and certainly if he does not.

Sources: Poskim who rule no need to pay back person who paid loan: Michaber and Rama C.M. 128:1; Shach 128:5; Rambam Malveh Veloveh 26:6; Kesubos 109a; Tur 128 in name of Rambam ibid; Rashi Nedarim 33b; Rif Kesubos 63b; Tosafos Kesubos 108a in name of Riva; Yerushalmi Kesubos 13:2; Nedarim 4:2;  Poskim who rule must pay back person who paid loan: Yeish Cholkim, brought and negated, in Rama C.M. 128:1; Tur 128:2 in name of Rabbeinu Tam Kesubos 108a; Rosh Kesubos 13:8; Maryu 166; Darkei Moshe 128:2; Rama ibid regarding if it was owed to gentile